Method and apparatus for performing random access procedure

ABSTRACT

A communication method and system for converging a fifth generation (5G) communication system for supporting higher data rates beyond a fourth generation (4G) system with a technology for internet of things (IoT) are provided. The communication method and system includes intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. A method by a terminal for transmitting a random access (RA) preamble is provided. The method includes receiving configuration information on RA resources associated with synchronization signal (SS) blocks from a base station, receiving one or more SS blocks from the base station, determining whether there is at least one suitable SS block for which contention free RA resources are configured amongst the one or more SS blocks based on the configuration information, selecting a suitable SS block for which contention free RA resources are configured if there is at least one suitable SS block for which contention free RA resources are configured amongst the one or more SS blocks, selecting a first RA preamble corresponding to the selected suitable SS block, and transmitting the first RA preamble to the base station.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based on and claims priority under 35 U.S.C. §119(a) of an Indian patent application number 201711026769, filed onJul. 27, 2017, in the Indian Patent Office, the disclosure of which isincorporated by reference herein in its entirety.

BACKGROUND 1. Field

The disclosure relates to a system, a method and an apparatus forperforming a random access procedure in a wireless communication system.More particularly, the disclosure relates to a method for selectingPRACH preamble and/or PRACH resources/occasions during the random accessprocedure.

2. Description of the Related Art

To meet the demand for wireless data traffic having increased sincedeployment of fourth generation (4G) communication systems, efforts havebeen made to develop an improved fifth generation (5G) or pre-5Gcommunication system. Therefore, the 5G or pre-5G communication systemis also called a ‘beyond 4G network’ or a ‘post long term evolution(LTE) System’. The 5G wireless communication system is considered to beimplemented not only in lower frequency bands but also in higherfrequency (mmWave) bands, e.g., 10 GHz to 100 GHz bands, so as toaccomplish higher data rates. These frequency bands can be licensed orunlicensed. To mitigate propagation loss of the radio waves and increasethe transmission distance, the beamforming, massive multiple-inputmultiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna,an analog beam forming, and large scale antenna techniques are beingconsidered in the design of the 5G wireless communication system. Inaddition, in 5G communication systems, development for system networkimprovement is under way based on advanced small cells, cloud radioaccess networks (RANs), ultra-dense networks, device-to-device (D2D)communication, wireless backhaul, moving network, cooperativecommunication, coordinated multi-points (CoMP), reception-endinterference cancellation and the like. In the 5G system, hybridfrequency shift keying (FSK) and quadrature amplitude modulation (QAM)(FQAM) and sliding window superposition coding (SWSC) as an advancedcoding modulation (ACM), filter bank multi carrier (FBMC),non-orthogonal multiple access (NOMA), and sparse code multiple access(SCMA) as an advanced access technology have been developed.

The Internet, which is a human centered connectivity network wherehumans generate and consume information, is now evolving to the internetof things (IoT) where distributed entities, such as things, exchange andprocess information without human intervention. The internet ofeverything (IoE), which is a combination of the IoT technology and thebig data processing technology through connection with a cloud server,has emerged. As technology elements, such as “sensing technology”,“wired/wireless communication and network infrastructure”, “serviceinterface technology”, and “Security technology” have been demanded forIoT implementation, a sensor network, a machine-to-machine (M2M)communication, machine type communication (MTC), and so forth have beenrecently researched. Such an IoT environment may provide intelligentInternet technology services that create a new value to human life bycollecting and analyzing data generated among connected things. IoT maybe applied to a variety of fields including smart home, smart building,smart city, smart car or connected cars, smart grid, health care, smartappliances and advanced medical services through convergence andcombination between existing information technology (IT) and variousindustrial applications.

In line with this, various attempts have been made to apply 5Gcommunication systems to IoT networks. For example, technologies, suchas a sensor network, MTC, and M2M communication may be implemented bybeamforming, MIMO, and array antennas. Application of a cloud RAN as theabove-described big data processing technology may also be considered tobe as an example of convergence between the 5G technology and the IoTtechnology.

In the recent years several broadband wireless technologies have beendeveloped to meet the growing number of broadband subscribers and toprovide more and better applications and services. The second generation(2G) wireless communication system has been developed to provide voiceservices while ensuring the mobility of users. The third generation (3G)wireless communication system supports not only the voice service butalso data service. The 4G wireless communication system has beendeveloped to provide high-speed data service. However, the 4G wirelesscommunication system suffers from lack of resources to meet the growingdemand for high speed data services. Therefore, the 5G wirelesscommunication system is being developed to meet the growing demand ofvarious services with diverse requirements, e.g., high speed dataservices, support ultra-reliability and low latency applications.

In addition, the 5G wireless communication system is expected to addressdifferent use cases having quite different requirements in terms of datarate, latency, reliability, mobility etc. However, it is expected thatthe design of the air-interface of the fifth generation wirelesscommunication system would be flexible enough to serve the userequipments (UEs) having quite different capabilities depending on theuse case and market segment the UE cater service to the end customer.Example use cases the 5G wireless communication system wireless systemis expected to address is enhanced mobile broadband (eMBB), massive MTC(m-MTC), ultra-reliable low latency communication (URLL), etc. The eMBBrequirements like tens of Gbps data rate, low latency, high mobility soon and so forth address the market segment representing the related-artwireless broadband subscribers desiring internet connectivityeverywhere, all the time and on the go. The m-MTC requirements like veryhigh connection density, infrequent data transmission, very long batterylife, low mobility address so on and so forth address the market segmentrepresenting the IoT/IoE envisioning connectivity of billions ofdevices. The URLL requirements like very low latency, very highreliability and variable mobility so on and so forth address the marketsegment representing the industrial automation application,vehicle-to-vehicle/vehicle-to-infrastructure communication foreseen asone of the enablers for autonomous cars.

In the existing wireless communication system i.e., in LTE, randomaccess (RA) procedure is used to achieve uplink time synchronization. RAprocedure is used in LTE during initial access, handover, radio resourcecontrol (RRC) connection re-establishment procedure, positioningpurpose, scheduling request transmission, secondary cell group (SCG)addition/modification and data or control information transmission inuplink by non-synchronized UE in RRC CONNECTED state. In LTE two typesof RA procedure are defined: contention-based and contention-free.

Contention-Based RA (CBRA) Procedure:

FIG. 1 illustrates a procedure of CBRA according to the related art.

RA Preamble (or Msg1) Transmission: UE transmits an RA preamble atoperation 101. UE selects one of the available 64-Ncf contention basedRA preambles. Ncf is the number of RA preambles reserved for contentionfree access. The contention based RA preambles can be optionallypartitioned into two groups. If two groups are configured, UE selectsthe group based on size of message 3 UE can transmit. The initial RApreamble transmission power is set based on open loop estimation aftercompensating for path loss.

RA response (RAR) or Msg2: Evolved node B (eNB) transmits the RAR onphysical downlink shared channel (PDSCH) addressed to randomaccess-radio network temporary identifier (RA-RNTI) at operation 102.RA-RNTI identifies the time-frequency slot in which RA preamble wasdetected by eNB. RAR conveys RA preamble identifier, timing alignmentinformation, temporary cell-radio network temporary identifier (C-RNTI)and UL grant for message 3. RAR may also include back off indicator toinstruct UE to back off for period of time before retrying RA attempt.RAR is transmitted in RAR window.

FIG. 3 illustrates an RA preamble transmission and an RAR windowaccording to the related art.

As shown in FIG. 3 , RAR window starts at subframe ‘x+3’ for RA preambletransmitted in subframe ‘x’. RAR window size is configurable.

Scheduled uplink (UL) Transmission on UL shared channel (SCH) (or Msg3):UE performs scheduled transmission at operation 103. The scheduled ULtransmission is used to transmit message such as RRC connection request,RRC connection re-establishment request, RRC handover confirm,scheduling request, etc. It also includes the UE identity (i.e., C-RNTIor system architecture evolution-temporary mobile subscriber identity(S-TMSI) or a random number). Hybrid automatic repeat request (HARQ) isused for this transmission. The message transmitted in the scheduled ULtransmission is commonly referred as Msg3.

Contention Resolution Message (or Msg 4): eNB transmits contentionresolution message at operation 104. The contention resolution messageis also commonly referred as Msg4. The contention resolution messageuses HARQ and is addressed to C-RNTI (if included in Msg3) or temporaryC-RNTI (if C-RNTI is not included in Msg3). On successful decoding ofthe contention resolution message, HARQ feedback is only sent by UEwhich detects its own UE ID (or C-RNTI).

Contention-Free RA (CFRA) Procedure:

FIG. 2 illustrates a procedure of CFRA according to the related art.

CFRA procedure is used for scenarios such as handover where low latencyis required, timing advance establishment for secondary cell (Scell),etc.

Referring to FIG. 2 , eNB assigns to UE a non-contention RA preamble indedicated signaling at operation 201.

The UE transmits the assigned non-contention RA preamble at operation202.

The eNB transmits the RAR on PDSCH addressed to RA-RNTI at operation203. RAR conveys RA preamble identifier and timing alignmentinformation. RAR may also include UL grant. RAR is transmitted in RARwindow similar to CBRA procedure. CFRA procedure terminates afterreceiving the RAR.

It is to be noted that during the random access procedure which iscontention free (i.e., contention free preamble is assigned), UEtransmits and retransmits the contention free RA preamble until therandom access procedure is completed.

Issue Description

At higher frequency, beamforming is necessary to compensate for highpath loss. UE/gNB needs to transmit/receive physical random accesschannel (PRACH) preamble and Msg3 using beamforming. GNB/UE needs totransmit/receive RAR & Msg4 using beamforming. UE and gNB may supportmultiple transmission (TX)/reception (RX) beams where each TX/RX beamcovers a specific coverage area. In case of beamformed PRACH preambletransmission, DL TX beam (i.e., gNB TX beam) is indicated by UE duringPRACH preamble transmission. Based on received PRACH preambletransmission, gNB can identify the DL TX beam for transmitting Msg2.

UE can identify the DL TX beam based on DL synchronization signals,reference signals or broadcast channel which are transmitted multipletimes in case of beamforming system. One or multiple DL TX beams can beused for transmitting DL synchronization signals, reference signals orbroadcast channel in each time occasion. A time occasion of transmittingsynchronization signals (i.e., primary synchronization signal(PSS)/synchronization signal (SSS) and primary broadcast channel (PBCH)using one or multiple DL TX beams is referred as synchronization signal(SS) block. Network transmits DL synchronization signals and PBCH usingmultiple SS blocks periodically. GNB can configure an associationbetween one or multiple occasion for SS Block and a subset of randomaccess channel (RACH) resources (i.e., time/frequency resources whichare also referred as PRACH occasions or RA occasions) and/or a subset ofPRACH preamble (also referred as RA preamble or Random Access preamble)indices. This association can be configured in RACH configurationsignaled in system information or in dedicated RRC signaling (e.g.,handover command). UE selects the PRACH preamble and/or PRACH resource(or PRACH occasion) corresponding to SS block in which the UE hasreceived the DL synchronization signals. Similar to SS blocks, gNB canconfigure an association between one or multiple CSI-RSs (CSI-RS istransmitted using TX beamforming) and a subset of PRACH resources (i.e.,time/frequency resources which are also referred as PRACH occasions orRA occasions) and/or a subset of PRACH preamble indices. Thisassociation can be configured in RACH configuration signaled in systeminformation or in dedicated RRC signaling (e.g., handover command). UEselects the PRACH preamble and/or PRACH resource (or PRACH occasion)corresponding to received CSI-RS signal.

The first issue is how the UE selects the SS block for PRACH preambleand/or PRACH resource (or PRACH occasion) selection during initial PRACHpreamble transmission. The second issue is how the UE selects the SSblock for PRACH preamble and/or PRACH resource (or PRACH occasion)selection during PRACH re-transmission i.e., when UE fails to receiveRAR successfully after transmitting the PRACH preamble. The third issueis how the UE selects the SS block for PRACH preamble and/or PRACHresource selection (or PRACH occasion) during handover to target cellfor PRACH (re-)transmission in target cell wherein the handover commandincludes contention free PRACH preambles and/or PRACH resources (orPRACH occasions) for one or more SS blocks in addition to contentionbased PRACH preambles and/or PRACH resources (or PRACH occasions) forall SS blocks.

The above information is presented as background information only toassist with an understanding of the disclosure. No determination hasbeen made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the disclosure.

SUMMARY

Aspects of the disclosure are to address at least the above-mentionedproblems and/or disadvantages and to provide at least the advantagesdescribed below. Accordingly, an aspect of the disclosure is to providea communication method and system for converging a fifth generation (5G)communication system for supporting higher data rates beyond a fourthgeneration (4G) system.

In accordance with a first aspect of the disclosure, a method by aterminal for transmitting a random access (RA) preamble is provided. Themethod includes receiving configuration information on RA resourcesassociated with synchronization signal (SS) blocks from a base station,receiving one or more SS blocks from the base station, identifyingwhether there is at least one suitable SS block for which contentionfree RA resources are configured amongst the one or more SS blocks,selecting a suitable SS block for which contention free RA resources areconfigured if there is at least one suitable SS block for whichcontention free RA resources are configured amongst the one or more SSblocks, selecting a first RA preamble corresponding to the selectedsuitable SS block, and transmitting the first RA preamble to the basestation.

In accordance with a second aspect of the disclosure, a method by a basestation for receiving a random access (RA) preamble. The method includestransmitting configuration information on RA resources associated withsynchronization signal (SS) blocks to a terminal, transmitting one ormore SS blocks to the terminal, and receiving an RA preamble from theterminal. The RA preamble corresponds to a SS block selected amongst theone or more SS blocks based on whether there is at least one suitable SSblock for which contention free RA resources are configured amongst theone or more SS blocks. The SS block is a suitable SS block for whichcontention free RA resources are configured if there is at least onesuitable SS block for which contention free RA resources are configuredamongst the one or more SS blocks.

In accordance with a third aspect of the disclosure, a terminal fortransmitting a random access (RA) preamble is provided. The terminalincludes a transceiver and a controller coupled with the transceiver.The transceiver is configured to receive signals from a base station,and transmit signals to the base station. The controller is configuredto control the transceiver to receive configuration information on RAresources associated with synchronization signal (SS) blocks from thebase station, control the transceiver to receive one or more SS blocksfrom the base station, identify whether there is at least one suitableSS block for which contention free RA resources are configured amongstthe one or more SS blocks, select a suitable SS block for whichcontention free RA resources are configured if there is at least onesuitable SS block for which contention free RA resources are configuredamongst the one or more SS blocks, select a first RA preamblecorresponding to the selected suitable SS block, and control thetransceiver to transmit the first RA preamble to the base station.

In accordance with a fourth aspect of the disclosure, a base station forreceiving a random access (RA) preamble is provided. The base stationincludes a transceiver and a controller coupled with the transceiver.The transceiver is configured to receive signals from a terminal, andtransmit signals to the terminal. The controller is configured tocontrol the transceiver to transmit configuration information on RAresources associated with synchronization signal (SS) blocks to theterminal, control the transceiver to transmit one or more SS blocks tothe terminal, and control the transceiver to receive an RA preamble fromthe terminal. The RA preamble corresponds to a SS block selected amongstthe one or more SS blocks based on whether there is at least onesuitable SS block for which contention free RA resources are configuredamongst the one or more SS block. The SS block is a suitable SS blockfor which contention free RA resources are configured if there is atleast one suitable SS block for which contention free RA resources areconfigured amongst the one or more SS blocks.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the disclosure will be more apparent from the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates a procedure of contention-based random access (RA)(CBRA) according to the related art;

FIG. 2 illustrates a procedure of contention-free RA (CFRA) according tothe related art;

FIG. 3 illustrates an RA preamble transmission and an RA response (RAR)window according to the related art;

FIG. 4 describes a user equipment (UE) behavior at a high levelaccording to an embodiment of the disclosure;

FIG. 5 illustrates a UE behavior for random access channel (RACH)transmission and re-transmission based on Method 1 according to anembodiment of the disclosure;

FIG. 6 illustrates a UE behavior for RACH transmission andre-transmission based on Method 2 according to an embodiment of thedisclosure;

FIG. 7 illustrates a UE behavior for RACH transmission andre-transmission based on Method 3 according to an embodiment of thedisclosure;

FIG. 8 illustrates a UE behavior for RACH transmission andre-transmission based on Method 4 according to an embodiment of thedisclosure;

FIG. 9 illustrates a UE behavior for RACH transmission andre-transmission based on Method 5 according to an embodiment of thedisclosure;

FIG. 10 illustrates a UE behavior for RACH transmission andre-transmission based on Method 6 according to an embodiment of thedisclosure;

FIG. 11 illustrates a UE behavior for RACH transmission andre-transmission based on Method 7 according to an embodiment of thedisclosure;

FIG. 12 illustrates a UE behavior for RACH transmission andre-transmission based on Method 8 according to an embodiment of thedisclosure;

FIG. 13 illustrates a UE behavior for RACH transmission andre-transmission based on Method 9 according to an embodiment of thedisclosure;

FIG. 14 illustrates a UE behavior for RACH transmission andre-transmission based on Method 10 according to an embodiment of thedisclosure;

FIG. 15 illustrates a UE behavior for RACH transmission andre-transmission based on Method 11 according to an embodiment of thedisclosure;

FIG. 16 illustrates a UE behavior for RACH transmission andre-transmission based on Method 12 according to an embodiment of thedisclosure;

FIG. 17 illustrates a UE behavior for RACH transmission andre-transmission based on Method 13 according to an embodiment of thedisclosure;

FIG. 18 illustrates a UE behavior for RACH transmission andre-transmission based on Method 14 according to an embodiment of thedisclosure;

FIG. 19 illustrates a UE behavior for RACH transmission andre-transmission based on Method 15 according to an embodiment of thedisclosure;

FIG. 20 illustrates a UE behavior for RACH transmission andre-transmission based on Method 16 according to an embodiment of thedisclosure;

FIG. 21 illustrates a UE behavior for RACH transmission andre-transmission based on Method 17 according to an embodiment of thedisclosure;

FIG. 22 illustrates a UE behavior for RACH transmission andre-transmission based on Method 18 according to an embodiment of thedisclosure;

FIG. 23 illustrates a UE behavior for RACH transmission andre-transmission based on Method 19 according to an embodiment of thedisclosure;

FIGS. 24A and 24B illustrate a UE behavior for RACH transmission andre-transmission based on Method 20 according to an embodiment of thedisclosure;

FIG. 25 illustrates an example where UE performs only one Msg. 1transmission before RAR window;

FIGS. 26A and 26B illustrate two examples of multiple Msg. 1transmissions before RAR window according to various embodiments of thedisclosure;

FIG. 27 illustrates multiple Msg1 transmissions before or while waitingfor RAR for first transmitted Msg1 based on Option 1 according to anembodiment of the disclosure;

FIGS. 28 and 29 illustrate multiple Msg1 transmissions before or whilewaiting for RAR for first transmitted Msg1 based on Option 2 accordingto an embodiment of the disclosure;

FIG. 30 illustrates multiple Msg1 transmissions before or while waitingfor RAR for first transmitted Msg1 based on Option 3 according to anembodiment of the disclosure;

FIG. 31 is a block diagram of a UE according to an embodiment of thedisclosure; and

FIG. 32 is a block diagram of a base station (BS) according to anembodiment of the disclosure.

Throughout the drawings, like reference numerals will be understood torefer to like parts, components, and structures.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thedisclosure. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of thedisclosure. Accordingly, it should be apparent to those skilled in theart that the following description of various embodiments of thedisclosure is provided for illustration purpose only and not for thepurpose of limiting the disclosure as defined by the appended claims andtheir equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to those ofskill in the art, may occur in amounts that do not preclude the effectthe characteristic was intended to provide.

It is known to those skilled in the art that blocks of a flowchart (orsequence diagram) and a combination of flowcharts may be represented andexecuted by computer program instructions. These computer programinstructions may be loaded on a processor of a general purpose computer,special purpose computer, or programmable data processing equipment.When the loaded program instructions are executed by the processor, theycreate a means for carrying out functions described in the flowchart.Because the computer program instructions may be stored in a computerreadable memory that is usable in a specialized computer or aprogrammable data processing equipment, it is also possible to createarticles of manufacture that carry out functions described in theflowchart. Because the computer program instructions may be loaded on acomputer or a programmable data processing equipment, when executed asprocesses, they may carry out operations of functions described in theflowchart.

A block of a flowchart may correspond to a module, a segment, or a codecontaining one or more executable instructions implementing one or morelogical functions, or may correspond to a part thereof. In some cases,functions described by blocks may be executed in an order different fromthe listed order. For example, two blocks listed in sequence may beexecuted at the same time or executed in reverse order.

In this description, the words “unit”, “module” or the like may refer toa software component or hardware component, such as, for example, afield-programmable gate array (FPGA) or an application-specificintegrated circuit (ASIC) capable of carrying out a function or anoperation. However, a “unit”, or the like, is not limited to hardware orsoftware. A unit, or the like, may be configured so as to reside in anaddressable storage medium or to drive one or more processors. Units, orthe like, may refer to software components, object-oriented softwarecomponents, class components, task components, processes, functions,attributes, procedures, subroutines, program code segments, drivers,firmware, microcode, circuits, data, databases, data structures, tables,arrays or variables. A function provided by a component and unit may bea combination of smaller components and units, and may be combined withothers to compose larger components and units. Components and units maybe configured to drive a device or one or more processors in a securemultimedia card.

Prior to the detailed description, terms or definitions necessary tounderstand the disclosure are described. However, these terms should beconstrued in a non-limiting way.

The “base station (BS)” is an entity communicating with a user equipment(UE) and may be referred to as BS, base transceiver station (BTS), nodeB (NB), evolved NB (eNB), access point (AP), 5G NB (5GNB), or gNB.

The “UE” is an entity communicating with a BS and may be referred to asUE, device, mobile station (MS), mobile equipment (ME), or terminal.

FIG. 4 describes the UE behavior at a high level according to anembodiment of the disclosure. The UE behavior described in FIG. 4 willbe discussed in detail in various methods discussed further below.

Referring to FIG. 4 , UE first decides whether the access latency is anissue or not for its random access channel (RACH) procedure at operation410. For example, for a low latency application, the UE definitely hasto finish its RACH procedure fast and hence access latency is definitelyan issue. However for some applications wherein the UE only worriesabout sending a report to the BS but is not worried about time taken forthe same, such as in metering applications, a UE can conclude that theaccess latency is not an issue for its network entry. When the accesslatency is indeed critical, the UE must enter the network as soon aspossible and hence the UE can decide to perform RACH on a suitable SSblock (the definition of suitable and how it is chosen will be discussedin detail later) at operation 420. Otherwise, the UE can find the bestSS block among all possible SS blocks transmitted by the gNB i.e., afterscanning and measuring all the SS blocks transmitted by the gNB(indicated via parameter L which is pre-defined for a given frequencyband in 3GPP specifications or indicated via parameter‘SSBPositionsInBurst’ signaled by gNB in system information or RRCmessage) and then take a decision at operation 430. Furthermore, thisdecision can also be extended to the UE side beamforming whether the UEmust scan all its UE reception (Rx) beams at operation 421 or 431, orthe UE can just choose one RX beam and be satisfied when the UE finds asuitable SS block corresponding to this chosen UE Rx beam at operation422 or 432. While the RACH procedure performance may indeed depend onthis choice of the SS block, the UE will mostly worry only about campingonto the network as soon as possible in case access latency is an issue.This procedure of finding suitable SS block can be either left to fullUE implementation or can be supported by the gNB or fixed in thespecification via an explicit threshold. The various methods by which areference signals received power (RSRP) threshold can be indicated tothe UE are discussed below. If reference signal received quality (RSRQ)measurements or signal-to-interference-plus-noise ratio (SINR)measurements will be used for the case of RACH procedure, the thresholdneeds to be indicated and signaled appropriately. For ease, it isdescribed only as a threshold in the rest of the disclosure.

For the case of initial access RACH procedure, the gNB can indicate thethreshold for selecting the SS block to the UE by one or combinations ofthe following mechanisms:

1. Fixed in specification.

2. remaining minimum system information (RMSI) (e.g., SIB 1) indication.

3. RACH configuration indication.

A gNB can have full control over its network loading, cell edge radius,deployment conditions etc. Hence, a gNB may decide to change thethreshold used for the suitable SS block choice, for various UEs, byexplicit indication via RMSI or via RACH configuration information. Avalue fixed in specification may or may not work at all situations.Furthermore, for fairness cases, the gNB may decide this thresholduniformly fairly across all users and hence explicit indication may bepreferable. This threshold may be explicitly indicated as an absolutevalue or as a differential value with respect to some reference valuesuch as −100 dBm (as an example) which may be fixed in specification.This differential reporting can help to reduce some number of bits inthe way this threshold is indicated.

For the case of sub-6 GHz systems, wherein the multiple SS blocks aremainly provided for the case of coherent combining and better PBCHdemodulation, it does not matter which RACH resource the UE chooses.This may be explicitly indicated to the user by the gNB. This issue ofchoosing the SS block makes a difference especially in the case ofmmWave systems wherein a UE must choose a specificbeam/direction/SS-block of the gNB for performing RACH.

4. For re-transmission; threshold can be indicated in RAR if somethingchanges at gNB side.

The same threshold indicated in the initial access procedure maycontinue to be used for the case of full RACH procedure and anyre-transmissions that may be needed for the same. Else, an explicitindication in the RAR message may be indicated to the UE which it canuse for further re-transmissions of the RACH preamble. This enablesflexibility from gNB side to dynamically change the threshold based onchannel conditions/network loading etc.

5. For contention-free (CF); indicate the threshold in handover commandfor the CSI-RS RACH.

6. For CF; this threshold is fixed in specification.

7. For CF; Complete UE implementation without target gNB assistance.

8. For CF; indicate the threshold in dedicated UE specific signaling.

For the case of CF RACH based on CSI-RS, a different threshold may haveto be indicated to the UE which is suitable for the CSI-RSresources/beams. This is because the CSI-RS beams may have a differentconfiguration as opposed to the SS block based beams i.e., wider versusnarrow etc. In such cases an appropriate threshold for the same alsohave to be indicated. Apart from (6) and (7) above which are similar tothe case of SS block, for the CF case, the target cell must indicate thethreshold to be used. Hence, this threshold may be indicated in thehandover command. For the case of this handover, as discussed next, thetarget cell may indicate two thresholds to the UE: a) CSI-RS basedthreshold and the b) SS-based threshold. Again, SS threshold can bedifferent from CSI-RS threshold due to difference in beam formingdesigns.

9. For CF case; fall back RACH based on SS-based threshold can beindicated in handover command.

10. For CF case; fall back RACH based on SS-based threshold can beindicated via SI of the target cell.

11. For CF case; fall back RACH based on SS-based threshold can be fixedin specification.

12. For CF case; fall back RACH based on SS-based threshold can beindicated via RACH configuration of the target cell.

The options 8-11 indicate the various means of indicating this SS-basedthreshold for the case of CF RACH performed in the case of the handoverprocedure. If the UE reads the system information (SI) of the targetcell, then this threshold may be indicated via SI as well. Also thisthreshold can be included in the RACH configuration of the target cellwhen the RACH configuration is provided to the UE.

13. SS threshold for initial access can be different from the SSthreshold for handover/CF case.

Note that the thresholds for the case of initial access and handover canbe different in order to support fast access to network or fasterhandover and low interruption times etc. For example, conservativethresholds may be provided in case of the handover to allow for 0 mshandover interruption times.

14. If no indication, UE assumes same threshold for initial access andhandover for SS based mechanisms.

If no explicit indication is given to the UE, then the UE can use theavailable threshold which was given in the previous stages, such asinitial access.

15. For the case of beam recovery RACH, which may be based on CSI-RS orSS-blocks; the threshold needed for the same can be indicated to the UEvia RRC connection establishment procedure (i.e., in RRC reconfigurationmessage).

This threshold for beam recovery may be different from the otherthresholds as the UE must recover fast from the beam failure via L1mechanisms. If the beam recovery is initiated by the network, then thethreshold can be indicated to the UE via UE specific signaling which issuitable for the specific time when the procedure is triggered i.e., viadownlink control information (DCI) or media access control (MAC) or RRCsignaling.

Having set the context for choosing best or suitable SS blocks, it isdescribed in detail the UE behavior for the RACH transmission andre-transmission by using the available measurements as below.

Method 1:

FIG. 5 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 1 according to an embodiment of thedisclosure.

Referring to FIG. 5 , UE selects the SS block with highest signalquality for initial PRACH preamble transmission at operation 501. Duringa random access procedure, the first PRACH preamble transmission isreferred as the initial PRACH preamble transmission. The signal qualityis measured over the resources of SS block carrying PSS and/or SSSand/or demodulation reference signal (DMRS) for PBCH. The signal qualitycan be RSRP, RSRQ or received signal strength indicator (RSSI). In anembodiment, the UE may select the SS block with highest signal qualityamongst all SS blocks transmitted by gNB. In another embodiment, the UEmay select the SS block with highest signal quality amongst all SSblocks for which measurements are available.

The UE then transmits a PRACH preamble (i.e., Msg1) by selecting a PRACHpreamble and/or a PRACH resource (or PRACH occasion) corresponding tothe selected SS block at operation 502. A PRACH preamble may be referredas a RA preamble or a RACH preamble.

If SS block is associated with PRACH preambles, the UE selects a PRACHpreamble randomly from the PRACH preambles corresponding to the selectedSS block. The UE may select the earliest available PRACH resource (orPRACH occasion) from configured PRACH resources (or PRACH occasions). Inan embodiment, the UE may select randomly one PRACH resource (or PRACHoccasion) from configured PRACH resources (or PRACH occasions). In casemultiple frequency division multiplexed PRACH resources (or PRACHoccasions) are available at the same time, the UE randomly selects withequal probability one PRACH resource (or PRACH occasion) from availablemultiple frequency division multiplexed PRACH resources (or PRACHoccasions).

If SS block is associated with PRACH resources (or PRACH occasions), theUE may select the earliest available PRACH resource (or PRACH occasion)from PRACH resources (or PRACH occasions) corresponding to the selectedSS block. In an embodiment, the UE may select randomly one PRACHresource (or PRACH occasion) from configured PRACH resources (or PRACHoccasions) corresponding to the selected SS block. In case multiplefrequency division multiplexed PRACH resources (or PRACH occasions) areavailable at the same time corresponding to the selected SS block, theUE randomly selects with equal probability one PRACH resource (or PRACHoccasion) from available multiple frequency division multiplexed PRACHresources (or PRACH occasions). The UE randomly selects with equalprobability a PRACH preamble from configured set of PRACH preambles.

If SS block is associated with PRACH preambles and PRACH resources, theUE selects a PRACH preamble randomly from the PRACH preamblescorresponding to the selected SS block. In an embodiment, the UE mayselect randomly one PRACH resource (or PRACH occasion) from configuredPRACH resources (or PRACH occasions) corresponding to the selected SSblock. The UE may select the earliest available PRACH resource (or PRACHoccasion) from PRACH resources (or PRACH occasions) corresponding to theselected SS block. In case multiple frequency division multiplexed PRACHresources (or PRACH occasion) are available at the same timecorresponding to the selected SS block, the UE randomly selects withequal probability one PRACH resource (or PRACH occasion) from availablemultiple frequency division multiplexed PRACH resources (or PRACHoccasions).

For calculating the power for transmitting the PRACH, the UE estimatesthe path loss based on signals received in the selected SS block. Aftertransmitting the Msg1, the UE determines whether a RAR (i.e., Msg2)corresponding to Msg1 transmission is successfully received at operation503. If the UE successfully receives the RAR, there is no need toretransmit Msg1 at operation 504. If the UE is not able to receive theRAR, the UE determines whether the UE has performed maximum number ofallowed Msg1 transmissions at operation 505. The UE retransmits the Msg1if the UE has not yet transmitted maximum number of allowed Msg1transmissions. If the UE has performed maximum number of allowed Msg1transmissions, the UE does not retransmit Msg1. During theretransmission, the UE does not reselect the SS block. The UE uses thesame SS block as selected for initial transmission. SS block is selectedwhen random access procedure is initiated and the same SS block is usedfor PRACH preamble and/or PRACH resource (or PRACH occasion) selectionand path loss estimation for all (re-)transmissions of Msg1 during arandom access procedure.

In an alternate embodiment of this method, instead of SS block, CSI-RScan be used. UE selects CSI-RS instead of SS block using same procedureas explained above for SS block. The UE may select PRACH preamble and/orPRACH resource (or PRACH occasion) from PRACH preambles and/or PRACHresources (or PRACH occasion) corresponding to the selected CSI-RS.

Key Point:

UE may select SS block (or CSI-RS) with highest signal quality whenrandom access procedure is initiated. UE may use the selected SS block(or CSI-RS) for PRACH preamble and/or PRACH resource (or PRACH occasion)selection and path loss estimation for all (re-)transmissions of Msg1during a random access procedure.

Method 2:

FIG. 6 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 2 according to an embodiment of thedisclosure.

Referring to FIG. 6 , UE selects a suitable SS block for initial PRACHpreamble transmission at operation 601. A SS block is suitable if signalquality of SS block is greater than the threshold ‘SSBlockThreshold’. Inan embodiment, a SS block is suitable if signal quality of SS block isgreater than or equal to a threshold ‘SSBlockThreshold’. TheSSBlockThreshold can be configured by network in system information(e.g., together with PRACH configuration or in RMSI) or handover commandor in dedicated RRC signaling. The signal quality is measured over theresources of SS block carrying PSS and/or SSS and/or DMRS for PBCH. Thesignal quality can be RSRP or RSRQ or RSSI. In case multiple SS blocksare suitable, the UE may select a SS block in one of the following ways:

UE may select the SS block with highest signal quality amongst thesuitable SS blocks.

UE may select the SS block corresponding to which RACH resource (orPRACH occasion) is available earliest in time amongst the suitable SSblocks.

UE may select randomly with equal probability one of the SS blockamongst the suitable SS blocks.

UE may select any SS block amongst the suitable SS blocks.

UE may select one of the following methods based on indication (can besignaled as part of PRACH configuration in SI and/or handover commandand/or in dedicated RRC signaling) from network: select the SS blockwith highest signal quality amongst the suitable SS blocks or select theSS block corresponding to which RACH resource (or PRACH occasion) isavailable earliest in time amongst the suitable SS blocks or selectrandomly with equal probability one of the SS block amongst the suitableSS blocks.

The UE then transmits a PRACH preamble (i.e., Msg1) by selecting a PRACHpreamble and/or a PRACH resource (or PRACH occasion) corresponding tothe selected SS block at operation 602.

If SS block is associated with PRACH preambles, the UE selects a PRACHpreamble randomly from the PRACH preambles corresponding to the selectedSS block. The UE may select the earliest available PRACH resource (orPRACH occasion) from configured PRACH resources (or PRACH occasions). Inan embodiment, the UE may select randomly one PRACH resource (or PRACHoccasion) from configured PRACH resources (or PRACH occasions). In casemultiple frequency division multiplexed PRACH resources (or PRACHoccasions) are available in time, the UE randomly selects with equalprobability one PRACH resource (or PRACH occasion) from availablemultiple frequency division multiplexed PRACH resources (or PRACHoccasions).

If SS block is associated with PRACH resources (or PRACH occasions), theUE may select the earliest available PRACH resource (or PRACH occasion)from the PRACH resources (or PRACH occasions) corresponding to theselected SS block. In an embodiment, the UE may select randomly onePRACH resource (or PRACH occasion) from configured PRACH resources (orPRACH occasions) corresponding to the selected SS block. In casemultiple frequency division multiplexed PRACH resources (or PRACHoccasions) are available corresponding to the selected SS block, the UErandomly selects with equal probability one PRACH resource (or PRACHoccasion) from available multiple frequency division multiplexed PRACHresources (or PRACH occasions). The UE randomly selects with equalprobability a PRACH preamble from configured set of PRACH preambles.

If SS block is associated with PRACH preambles and PRACH resources, theUE selects a PRACH preamble randomly from the PRACH preamblescorresponding to the selected SS block. The UE may select the earliestavailable PRACH resource (or PRACH occasion) from PRACH resources (orPRACH occasions) corresponding to the selected SS block. In anembodiment, the UE may select randomly one PRACH resource (or PRACHoccasion) from configured PRACH resources (or PRACH occasions)corresponding to the selected SS block. In case multiple frequencydivision multiplexed PRACH resources (or PRACH occasion) are availablecorresponding to the selected SS block, the UE randomly selects withequal probability one PRACH resource (or PRACH occasion) from availablemultiple frequency division multiplexed PRACH resources (or PRACHoccasions).

For calculating the power for transmitting the PRACH, the UE estimatesthe path loss based on signals received in the selected SS block. Aftertransmitting the Msg1, the UE determines whether a RAR (i.e., Msg2)corresponding to Msg1 transmission is successfully received at operation603. If the UE successfully receives the RAR, there is no need toretransmit Msg1 at operation 604. If the UE is not able to receive theRAR, the UE determines whether the UE has performed maximum number ofallowed Msg1 transmissions at operation 605. The UE retransmits the Msg1if the UE has not yet transmitted maximum number of allowed Msg1transmissions. If the UE has performed maximum number of allowed Msg1transmissions, the UE does not retransmit Msg1. During theretransmission, the UE does not reselect the SS block. The UE uses thesame SS block as selected for initial transmission. Suitable SS block isselected when random access procedure is initiated and the same SS blockis used for PRACH preamble and/or PRACH resource (or PRACH occasion)selection and path loss estimation for all (re-)transmissions of Msg1during a random access procedure. In case suitable SS block is notfound, UE may reselect a suitable SS block during retransmission asexplained later.

In the procedure explained above, it is possible that the UE is not ableto find any suitable SS block. In this case the UE may perform one ofthe following:

The UE does not transmit Msg1. Additionally, the UE may trigger cellreselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state.

The UE selects SS block with highest signal quality among all the SSblocks or among the SS blocks for which measurements are available. Inthis case (i.e., when suitable SS block is not selected), duringretransmission of Msg1 the UE may change SS block if SS block forprevious transmission is still not suitable and another suitable SSblock is found. In an embodiment, the UE may be allowed to transmit Msg1without selecting a suitable SS block for ‘N’ number of times. ParameterN can be pre-defined or signaled by network.

The UE may delay Msg1 transmission until the UE founds suitable SSblock. In one embodiment, the UE may delay Msg1 transmission for amaximum time period ‘T’. The time period T can be configured by networkin system information (e.g., together with PRACH configuration or inRMSI) or handover command or in dedicated RRC signaling. After expiry ofthis time if suitable SS block is still not found the UE may triggercell reselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state. Alternately, after expiry of thistime if suitable SS block is still not found, the UE may select SS blockwith highest signal quality among all the SS blocks or among the SSblocks for which measurements are available.

In an alternate embodiment of this method, instead of SS block, CSI-RScan be used. UE selects CSI-RS instead of SS block using same procedureas explained above for SS block. The UE may select PRACH preamble and/orPRACH resource (or PRACH occasion) from PRACH preambles and/or PRACHresources (or PRACH occasion) corresponding to the selected CSI-RS.

Key Point:

1. UE may select suitable (signal quality>SSBlockThreshold) SS block (orCSI-RS) when random access procedure is initiated. UE may use theselected SS block (or CSI-RS) for PRACH preamble and/or PRACH resource(or PRACH occasion) selection and path loss estimation for all(re-)transmissions of Msg1 during a random access procedure.

2. UE may select SS block (or CSI-RS) with highest signal quality ifsuitable SS block is not found.

3. UE may change the SS block (or CSI-RS) if suitable SS block (orCSI-RS) was not used for previous transmission and SS block (or CSI-RS)for previous transmission is still not suitable and another suitable SSblock (or CSI-RS) is found.

4. UE may reselect the cell if suitable SS block (or CSI-RS) is notfound.

5. UE may delay the Msg1 transmission until suitable SS block (orCSI-RS) is found.

6. UE may delay the Msg1 transmission for a defined time period ifsuitable SS block (or CSI-RS) is not found. UE may trigger cellreselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state if suitable SS block (or CSI-RS)is not found even after that time period.

Method 3:

FIG. 7 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 3 according to an embodiment of thedisclosure.

Referring to FIG. 7 , UE selects the SS block with highest signalquality for initial PRACH preamble transmission at operation 701. Thesignal quality is measured over the resources of SS block carrying PSSand/or SSS and/or DMRS for PBCH. The signal quality can be RSRP or RSRQor RSSI. In an embodiment, the UE may select the SS block with highestsignal quality amongst all SS blocks transmitted by gNB. In anotherembodiment, the UE may select the SS block with highest signal qualityamongst all SS blocks for which measurements are available.

The UE then transmits a PRACH preamble (i.e., Msg1) by selecting a PRACHpreamble and/or a PRACH resource (or PRACH occasion) corresponding tothe selected SS block at operation 702.

If SS block is associated with PRACH preambles, the UE selects a PRACHpreamble randomly from the PRACH preambles corresponding to the selectedSS block. The UE may select the earliest available PRACH resource (orPRACH occasion) from configured PRACH resources (or PRACH occasions). Inan embodiment, the UE may select randomly one PRACH resource (or PRACHoccasion) from configured PRACH resources (or PRACH occasions). In casemultiple frequency division multiplexed PRACH resources (or PRACHoccasions) are available at the same time, the UE randomly selects withequal probability one PRACH resource (or PRACH occasion) from availablemultiple frequency division multiplexed PRACH resources (or PRACHoccasions).

If SS block is associated with PRACH resources (or PRACH occasions), theUE may select the earliest available PRACH resource (or PRACH occasion)from PRACH resources (or PRACH occasions) corresponding to the selectedSS block. In an embodiment, the UE may select randomly one PRACHresource (or PRACH occasion) from configured PRACH resources (or PRACHoccasions) corresponding to the selected SS block. In case multiplefrequency division multiplexed PRACH resources (or PRACH occasions) areavailable in time corresponding to the selected SS block, the UErandomly selects with equal probability one PRACH resource (or PRACHoccasion) from available multiple frequency division multiplexed PRACHresources (or PRACH occasions). The UE randomly selects with equalprobability a PRACH preamble from configured set of PRACH preambles.

If SS block is associated with PRACH preambles and PRACH resources, theUE selects a PRACH preamble randomly from the PRACH preamblescorresponding to the selected SS block. The UE may select the earliestavailable PRACH resource (or PRACH occasion) from PRACH resources (orPRACH occasions) corresponding to the selected SS block. In anembodiment, the UE may select randomly one PRACH resource (or PRACHoccasion) from configured PRACH resources (or PRACH occasions)corresponding to the selected SS block. In case multiple frequencydivision multiplexed PRACH resources (or PRACH occasion) are availablecorresponding to the selected SS block, the UE randomly selects withequal probability one PRACH resource (or PRACH occasion) from availablemultiple frequency division multiplexed PRACH resources (or PRACHoccasions).

For calculating the power for transmitting the PRACH, the UE estimatesthe path loss based on signals received in the selected SS block. Aftertransmitting the Msg1, the UE determines whether a RAR (i.e., Msg2)corresponding to Msg1 transmission is successfully received at operation703. If the UE successfully receives the RAR, there is no need toretransmit Msg1 at operation 704. If the UE is not able to receive theRAR, the UE determines whether the UE has performed maximum number ofallowed Msg1 transmissions at operation 705. The UE retransmits the Msg1if the UE has not yet transmitted maximum number of allowed Msg1transmissions. If the UE has performed maximum number of allowed Msg1transmissions, the UE does not retransmit Msg1. During theretransmission, the UE determines whether signal quality of SS blockselected for previous Msg1 transmission is greater than or equal to athreshold ‘SSBlockThreshold’ at operation 706. If the signal quality ofthe SS block selected for the previous Msg1 transmission is greater thanor equal to the threshold ‘SSBlockThreshold’ UE does not reselect the SSblock. The threshold can be configured by network in system information(e.g., together with PRACH configuration or in RMSI) or handover commandor in dedicated RRC signaling. The UE uses the same SS block as selectedfor the previous transmission for PRACH preamble and/or PRACH resourceselection and path loss estimation for retransmission (i.e., next Msg1transmission). During the retransmission, if the signal quality of theSS block selected for the previous Msg1 transmission is less than thethreshold ‘SSBlockThreshold’, the UE may reselect SS block at operation707. The UE may select the SS block with highest signal quality amongstall SS blocks transmitted by gNB. In another embodiment, the UE mayselect the SS block with highest signal quality amongst all SS blocksfor which measurements are available.

In an alternate embodiment of this method, instead of SS block, CSI-RScan be used. UE selects CSI-RS instead of SS block using same procedureas explained above for SS block. The UE may select PRACH preamble and/orPRACH resource (or PRACH occasion) from PRACH preambles and/or PRACHresources (or PRACH occasion) corresponding to the selected CSI-RS.

Key Point:

UE may select SS block (or CSI-RS) with highest signal quality whenrandom access procedure is initiated. UE reselects SS block (or CSI-RS)during retransmission if SS block (or CSI-RS) of previous transmissionis below a threshold based on latest measurement wherein SS block (orCSI-RS) with highest signal quality is selected during retransmission.UE may use the selected SS block (or CSI-RS) for PRACH preamble and/orPRACH resource (or PRACH occasion) selection and path loss estimationfor transmission of Msg1 during a random access procedure.

Method 4:

FIG. 8 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 4 according to an embodiment of thedisclosure.

Referring to FIG. 8 , UE selects the SS block with highest signalquality for initial PRACH preamble transmission at operation 801. Thesignal quality is measured over the resources of SS block carrying PSSand/or SSS and/or DMRS for PBCH. The signal quality can be RSRP or RSRQor RSSI. In an embodiment, the UE may select the SS block with highestsignal quality amongst all SS blocks transmitted by gNB. In anotherembodiment, the UE may select the SS block with highest signal qualityamongst all SS blocks for which measurements are available.

The UE then transmits a PRACH preamble (i.e., Msg1) by selecting a PRACHpreamble and/or a PRACH resource (or PRACH occasion) corresponding tothe selected SS block at operation 802.

If SS block is associated with PRACH preambles, the UE selects a PRACHpreamble randomly from the PRACH preambles corresponding to the selectedSS block. The UE may select the earliest available PRACH resource (orPRACH occasion) from configured PRACH resources (or PRACH occasions). Inan embodiment, the UE may select randomly one PRACH resource (or PRACHoccasion) from configured PRACH resources (or PRACH occasions). In casemultiple frequency division multiplexed PRACH resources (or PRACHoccasions) are available, the UE randomly selects with equal probabilityone PRACH resource (or PRACH occasion) from available multiple frequencydivision multiplexed PRACH resources (or PRACH occasions).

If SS block is associated with PRACH resources (or PRACH occasions), theUE may select the earliest available PRACH resource (or PRACH occasion)from PRACH resources (or PRACH occasions) corresponding to the selectedSS block. In an embodiment, the UE may select randomly one PRACHresource (or PRACH occasion) from configured PRACH resources (or PRACHoccasions) corresponding to the selected SS block. In case multiplefrequency division multiplexed PRACH resources (or PRACH occasions) areavailable in time corresponding to the selected SS block, the UErandomly selects with equal probability one PRACH resource (or PRACHoccasion) from available multiple frequency division multiplexed PRACHresources (or PRACH occasions). The UE randomly selects with equalprobability a PRACH preamble from configured set of PRACH preambles.

If SS block is associated with PRACH preambles and PRACH resources (orPRACH occasions), the UE selects a PRACH preamble randomly from thePRACH preambles corresponding to the selected SS block. The UE mayselect the earliest available PRACH resource (or PRACH occasion) fromPRACH resources (or PRACH occasions) corresponding to the selected SSblock. In an embodiment, the UE may select randomly one PRACH resource(or PRACH occasion) from configured PRACH resources (or PRACH occasions)corresponding to the selected SS block. In case multiple frequencydivision multiplexed PRACH resources (or PRACH occasion) are availabletime corresponding to the selected SS block, the UE randomly selectswith equal probability one PRACH resource (or PRACH occasion) fromavailable multiple frequency division multiplexed PRACH resources (orPRACH occasions).

For calculating the power for transmitting the PRACH, the UE estimatesthe path loss based on signals received in the selected SS block. Aftertransmitting the Msg1, the UE determines whether a RAR (i.e., Msg2)corresponding to Msg1 transmission is successfully received at operation803. If the UE successfully receives the RAR, there is no need toretransmit Msg1 at operation 804. If the UE is not able to receive theRAR, the UE determines whether the UE has performed maximum number ofallowed Msg1 transmissions at operation 805. The UE retransmits the Msg1if the UE has not yet transmitted maximum number of allowed Msg1transmissions. If the UE has performed maximum number of allowed Msg1transmissions, the UE does not retransmit Msg1. During theretransmission, the UE determines whether signal quality of SS blockselected for previous Msg1 transmission has the highest signalingquality based on latest measurements at operation 806. If the signalquality of the SS block selected for the previous Msg1 transmission hasthe highest signaling quality, the UE does not reselect the SS block.The UE uses the same SS block as selected for the previous transmissionfor PRACH preamble and/or PRACH resource selection and path lossestimation for retransmission (i.e., next Msg1 transmission). During theretransmission, if the signal quality of the SS block selected for theprevious Msg1 transmission does not have highest signaling quality, theUE may reselect SS block at operation 807. The UE may select the SSblock with highest signal quality amongst all SS blocks transmitted bygNB. In another embodiment, the UE may select the SS block with highestsignal quality amongst all SS blocks for which measurements areavailable.

In an alternate embodiment of this method, instead of SS block, CSI-RScan be used. UE selects CSI-RS instead of SS block using same procedureas explained above for SS block. The UE may select PRACH preamble and/orPRACH resource (or PRACH occasion) from PRACH preambles and/or PRACHresources (or PRACH occasion) corresponding to the selected CSI-RS.

Key Point:

UE may select SS block (or CSI-RS) with highest signal quality whenrandom access procedure is initiated. UE reselects SS block (or CSI-RS)during retransmission if SS block (or CSI-RS) of previous transmissiondoes not have highest signal quality based on latest measurement whereinSS block (or CSI-RS) with highest signal quality is selected duringretransmission. UE may use the selected SS block (or CSI-RS) for PRACHpreamble and/or PRACH resource (or PRACH occasion) selection and pathloss estimation for transmission of Msg1 during a random accessprocedure.

Method 5:

FIG. 9 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 5 according to an embodiment of thedisclosure.

Referring to FIG. 9 , UE selects a suitable SS block for initial PRACHpreamble transmission at operation 901. A SS block is suitable if signalquality of SS block is greater than the threshold ‘SSBlockThreshold’. Inan embodiment, a SS block is suitable if signal quality of SS block isgreater than or equal to a threshold ‘SSBlockThreshold’. TheSSBlockThreshold can be configured by network in system information(e.g., together with PRACH configuration or in RMSI) or handover commandor in dedicated RRC signaling. The signal quality is measured over theresources of SS block carrying PSS and/or SSS and/or DMRS for PBCH. Thesignal quality can be RSRP or RSRQ or RSSI. In case multiple SS blocksare suitable, the UE may select a SS block in one of the following ways:

UE may select the SS block with highest signal quality amongst thesuitable SS blocks.

UE may select the SS block corresponding to which RACH resource (orPRACH occasion) is available earliest in time amongst the suitable SSblocks.

UE may select randomly with equal probability one of the SS blockamongst the suitable SS blocks.

UE may select any SS block amongst the suitable SS blocks.

UE may select one of the following methods based on indication (can besignaled as part of PRACH configuration in SI and/or handover commandand/or in dedicated RRC signaling) from network: select the SS blockwith highest signal quality amongst the suitable SS blocks or select theSS block corresponding to which RACH resource (or PRACH occasion) isavailable earliest in time amongst the suitable SS blocks or selectrandomly with equal probability one of the SS block amongst the suitableSS blocks.

The UE then transmits a PRACH preamble (i.e., Msg1) by selecting a PRACHpreamble and/or a PRACH resource (or PRACH occasion) corresponding tothe selected SS block at operation 902.

If SS block is associated with PRACH preambles, the UE selects a PRACHpreamble randomly from the PRACH preambles corresponding to the selectedSS block. The UE may select the earliest available PRACH resource (orPRACH occasion) from configured PRACH resources (or PRACH occasions). Inan embodiment, the UE may select randomly one PRACH resource (or PRACHoccasion) from configured PRACH resources (or PRACH occasions). In casemultiple frequency division multiplexed PRACH resources (or PRACHoccasions) are available, the UE randomly selects with equal probabilityone PRACH resource (or PRACH occasion) from available multiple frequencydivision multiplexed PRACH resources (or PRACH occasions).

If SS block is associated with PRACH resources (or PRACH occasions), theUE may select the earliest available PRACH resource (or PRACH occasion)from PRACH resources (or PRACH occasions) corresponding to the selectedSS block. In an embodiment, the UE may select randomly one PRACHresource (or PRACH occasion) from configured PRACH resources (or PRACHoccasions) corresponding to the selected SS block. In case multiplefrequency division multiplexed PRACH resources (or PRACH occasions) areavailable in time corresponding to the selected SS block, the UErandomly selects with equal probability one PRACH resource (or PRACHoccasion) from available frequency division multiplexed PRACH resources(or PRACH occasions). The UE randomly selects with equal probability aPRACH preamble from configured set of PRACH preambles.

If SS block is associated with PRACH preambles and PRACH resources (orPRACH occasions), the UE selects a PRACH preamble randomly from thePRACH preambles corresponding to the selected SS block. The UE mayselect the earliest available PRACH resource (or PRACH occasion) fromPRACH resources (or PRACH occasions) corresponding to the selected SSblock. In an embodiment, the UE may select randomly one PRACH resource(or PRACH occasion) from configured PRACH resources (or PRACH occasions)corresponding to the selected SS block. In case multiple frequencydivision multiplexed PRACH resources (or PRACH occasion) are availablein time corresponding to the selected SS block, the UE randomly selectswith equal probability one PRACH resource (or PRACH occasion) fromavailable frequency division multiplexed PRACH resources (or PRACHoccasions).

For calculating the power for transmitting the PRACH, the UE estimatesthe path loss based on signals received in the selected SS block. Aftertransmitting the Msg1, the UE determines whether a RAR (i.e., Msg2)corresponding to Msg1 transmission is successfully received at operation903. If the UE successfully receives the RAR, there is no need toretransmit Msg1 at operation 904. If UE is not able to receive the RAR,the UE determines whether the UE has performed maximum number of allowedMsg1 transmissions at operation 905. The UE retransmits the Msg1 if theUE has not yet transmitted maximum number of allowed Msg1 transmissions.If the UE has performed maximum number of allowed Msg1 transmissions,the UE does not retransmit Msg1. During the retransmission, the UEdetermines whether signal quality of SS block selected for previous Msg1transmission is greater than or equal to a threshold ‘SSBlockThreshold’at operation 906. If the signal quality of the SS block selected for theprevious Msg1 transmission is greater than or equal to the threshold‘SSBlockThreshold’ the UE does not reselect the SS block. The thresholdcan be configured by network in system information (e.g., together withPRACH configuration or in RMSI) or handover command or in dedicated RRCsignaling. The UE uses the same SS block as selected for the previoustransmission for PRACH preamble and/or PRACH resource selection and pathloss estimation for retransmission (i.e., next Msg1 transmission).During the retransmission, if the signal quality of the SS blockselected for the previous Msg1 transmission is less than the threshold‘SSBlockThreshold’, the UE may reselect SS block at operation 907. TheUE may select a suitable SS block in same manner as the UE selected SSblock for initial Msg1 transmission. In an alternate embodiment, duringretransmission UE may select the SS block in same manner as initialtransmission.

In the procedure explained above, it is possible that the UE is not ableto find any suitable SS block. In this case the UE may perform one ofthe following:

The UE does not transmit Msg1. Additionally, the UE may trigger cellreselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state.

The UE selects SS block with highest signal quality among all the SSblocks or among the SS blocks for which measurements are available. Inthis case (i.e., when suitable SS block is not selected), duringretransmission of Msg1 the UE may change SS block if SS block forprevious transmission is still not suitable and another suitable SSblock is found. In an embodiment, the UE may be allowed to transmit Msg1without selecting a suitable SS block for ‘N’ number of times. ParameterN can be pre-defined or signaled by network.

The UE may delay Msg1 transmission until the UE founds suitable SSblock. In one embodiment, the UE may delay Msg1 transmission for amaximum time period ‘T’. The time period T can be configured by networkin system information (e.g., together with PRACH configuration or inRMSI) or handover command or in dedicated RRC signaling. After expiry ofthis time if suitable SS block is still not found the UE may triggercell reselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state. Alternately, after expiry of thistime if suitable SS block is still not found, the UE may select SS blockwith highest signal quality among all the SS blocks or among the SSblocks for which measurements are available.

In an alternate embodiment of this method, instead of SS block, CSI-RScan be used. UE selects CSI-RS instead of SS block using same procedureas explained above for SS block. The UE may select PRACH preamble and/orPRACH resource (or PRACH occasion) from PRACH preambles and/or PRACHresources (or PRACH occasion) corresponding to the selected CSI-RS.

Key Point:

1. UE may select suitable SS block (or CSI-RS) when random accessprocedure is initiated. UE reselects SS block (or CSI-RS) duringretransmission if SS block (or CSI-RS) of previous transmission is belowa threshold based on latest measurement wherein suitable SS block (orCSI-RS) is selected during retransmission. UE may use the selected SSblock (or CSI-RS) for PRACH preamble and/or PRACH resource (or PRACHoccasion) selection and path loss estimation for transmission of Msg1during a random access procedure.

2. UE may select SS block (or CSI-RS) with highest signal quality ifsuitable SS block is not found.

3. UE may change the SS block (or CSI-RS) if suitable SS block (orCSI-RS) was not used for previous transmission and SS block (or CSI-RS)for previous transmission is still not suitable and another suitable SSblock (or CSI-RS) is found.

4. UE may reselect the cell if suitable SS block (or CSI-RS) is notfound.

5. UE may delay the Msg1 transmission until suitable SS block (orCSI-RS) is found.

6. UE may delay the Msg1 transmission for a defined time period ifsuitable SS block (or CSI-RS) is not found. UE may trigger cellreselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state if suitable SS block (or CSI-RS)is not found even after that time period.

Method 6:

FIG. 10 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 6 according to an embodiment of thedisclosure.

Referring to FIG. 10 , UE selects a suitable SS block for initial PRACHpreamble transmission at operation 1001. A SS block is suitable ifsignal quality of SS block is greater than the threshold‘SSBlockThreshold’. In an embodiment, a SS block is suitable if signalquality of SS block is greater than or equal to a threshold‘SSBlockThreshold’. The SSBlockThreshold can be configured by network insystem information (e.g., together with PRACH configuration or in RMSI)or handover command or in dedicated RRC signaling. The signal quality ismeasured over the resources of SS block carrying PSS and/or SSS and/orDMRS for PBCH. The signal quality can be RSRP or RSRQ or RSSI. In casemultiple SS blocks are suitable, the UE may select a SS block in one ofthe following ways:

UE may select the SS block with highest signal quality amongst thesuitable SS blocks.

UE may select the SS block corresponding to which RACH resource (orPRACH occasion) is available earliest in time amongst the suitable SSblocks.

UE may select randomly with equal probability one of the SS blockamongst the suitable SS blocks.

UE may select any SS block amongst the suitable SS blocks.

UE may select one of the following methods based on indication (can besignaled as part of PRACH configuration in SI and/or handover commandand/or in dedicated RRC signaling) from network: select the SS blockwith highest signal quality amongst the suitable SS blocks or select theSS block corresponding to which RACH resource (or PRACH occasion) isavailable earliest in time amongst the suitable SS blocks or selectrandomly with equal probability one of the SS block amongst the suitableSS blocks.

The UE then transmits a PRACH preamble (i.e., Msg1) by selecting a PRACHpreamble and/or a PRACH resource (or PRACH occasion) corresponding tothe selected SS block at operation 1002.

If SS block is associated with PRACH preambles, the UE selects a PRACHpreamble randomly from the PRACH preambles corresponding to the selectedSS block. The UE may select the earliest available PRACH resource (orPRACH occasion) from configured PRACH resources (or PRACH occasions). Inan embodiment, the UE may select randomly one PRACH resource (or PRACHoccasion) from configured PRACH resources (or PRACH occasions). In casemultiple PRACH resources (or PRACH occasions) are available in time, theUE randomly selects with equal probability one PRACH resource (or PRACHoccasion) from available PRACH resources (or PRACH occasions).

If SS block is associated with PRACH resources (or PRACH occasions), theUE may select the earliest available PRACH resource (or PRACH occasion)from PRACH resources (or PRACH occasions) corresponding to the selectedSS block. In an embodiment, the UE may select randomly one PRACHresource (or PRACH occasion) from configured PRACH resources (or PRACHoccasions) corresponding to the selected SS block. In case multiplePRACH resources (or PRACH occasions) are available in time correspondingto the selected SS block, the UE randomly selects with equal probabilityone PRACH resource (or PRACH occasion) from available PRACH resources(or PRACH occasions). The UE randomly selects with equal probability aPRACH preamble from configured set of PRACH preambles.

If SS block is associated with PRACH preambles and PRACH resources(PRACH occasions), the UE selects a PRACH preamble randomly from thePRACH preambles corresponding to the selected SS block. The UE mayselect the earliest available PRACH resource (or PRACH occasion) fromPRACH resources (or PRACH occasions) corresponding to the selected SSblock. In an embodiment, the UE may select randomly one PRACH resource(or PRACH occasion) from configured PRACH resources (or PRACH occasions)corresponding to the selected SS block. In case multiple PRACH resources(or PRACH occasion) are available in time corresponding to the selectedSS block, the UE randomly selects with equal probability one PRACHresource (or PRACH occasion) from available PRACH resources (or PRACHoccasions).

For calculating the power for transmitting the PRACH, the UE estimatesthe path loss based on signals received in the selected SS block. Aftertransmitting the Msg1, the UE determines whether a RAR (i.e., Msg2)corresponding to Msg1 transmission is successfully received at operation1003. If the UE successfully receives the RAR, there is no need toretransmit Msg1 at operation 1004. If the UE is not able to receive theRAR, the UE determines whether the UE has performed maximum number ofallowed Msg1 transmissions at operation 1005. The UE retransmits theMsg1 if the UE has not yet transmitted maximum number of allowed Msg1transmissions. If the UE has performed maximum number of allowed Msg1transmissions, the UE does not retransmit Msg1. During theretransmission, the UE determines whether signal quality of SS blockselected for the previous Msg1 transmission has the best signal qualityamongst the available or all SS blocks measurement at operation 1006. Ifthe signal quality of the SS block selected for the previous Msg1transmission has the best signal quality amongst the available or all SSblocks measurement, the UE does not reselect the SS block. Otherwise theUE may reselect a suitable SS block in same manner as the UE selected SSblock for initial Msg1 transmission at operation 1007. In alternateembodiment, during the retransmission, if the signal quality of the SSblock selected for the previous Msg1 transmission is not above‘SSBlockThreshold’ and does not have the best signal quality amongst theavailable or all SS blocks measurements, the UE may reselect the SSblock in same manner as the UE selected SS block for initial Msg1transmission. Otherwise the UE does not reselect the SS block. Thethreshold can be configured by network in system information (e.g.,together with PRACH configuration or in RMSI) or handover command or indedicated RRC signaling.

In the procedure explained above, it is possible that the UE is not ableto find any suitable SS block. In this case the UE may perform one ofthe following:

The UE does not transmit Msg1. Additionally, the UE may trigger cellreselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state.

The UE selects SS block with highest signal quality among all the SSblocks or among the SS blocks for which measurements are available. Inthis case (i.e., when suitable SS block is not selected), duringretransmission of Msg1 the UE may change SS block if SS block forprevious transmission is still not suitable and another suitable SSblock is found. In an embodiment, the UE may be allowed to transmit Msg1without selecting a suitable SS block for ‘N’ number of times. ParameterN can be pre-defined or signaled by network.

The UE may delay Msg1 transmission until the UE founds suitable SSblock. In one embodiment, the UE may delay Msg1 transmission for amaximum time period ‘T’. The time period T can be configured by networkin system information (e.g., together with PRACH configuration or inRMSI) or handover command or in dedicated RRC signaling. After expiry ofthis time if suitable SS block is still not found the UE may triggercell reselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state. Alternately, after expiry of thistime if suitable SS block is still not found, the UE may select SS blockwith highest signal quality among all the SS blocks or among the SSblocks for which measurements are available.

In an alternate embodiment of this method, instead of SS block, CSI-RScan be used. UE selects CSI-RS instead of SS block using same procedureas explained above for SS block. The UE may select PRACH preamble and/orPRACH resource (or PRACH occasion) from PRACH preambles and/or PRACHresources (or PRACH occasion) corresponding to the selected CSI-RS.

Key Point:

1. UE may select suitable SS block (or CSI-RS) when random accessprocedure is initiated. UE reselects SS block (or CSI-RS) duringretransmission if SS block (or CSI-RS) of previous transmission is notthe best among the available SS block (or CSI-RS) measurements. UE mayuse the selected SS block (or CSI-RS) for PRACH preamble and/or PRACHresource (or PRACH occasion) selection and path loss estimation fortransmission of Msg1 during a random access procedure.

2. UE may select suitable SS block (or CSI-RS) when random accessprocedure is initiated. UE reselects SS block (or CSI-RS) duringretransmission if signal quality of SS block selected for previous Msg1transmission is not above ‘SSBlockThreshold’ and does not have the bestsignal quality amongst the available or all SS blocks measurements. UEmay use the selected SS block (or CSI-RS) for PRACH preamble and/orPRACH resource (or PRACH occasion) selection and path loss estimationfor transmission of Msg1 during a random access procedure.

3. UE may select SS block (or CSI-RS) with highest signal quality ifsuitable SS block is not found.

4. UE may change the SS block (or CSI-RS) if suitable SS block (orCSI-RS) was not used for previous transmission and SS block (or CSI-RS)for previous transmission is still not suitable and another suitable SSblock (or CSI-RS) is found.

5. UE may reselect the cell if suitable SS block (or CSI-RS) is notfound.

6. UE may delay the Msg1 transmission until suitable SS block (orCSI-RS) is found.

7. UE may delay the Msg1 transmission for a defined time period ifsuitable SS block (or CSI-RS) is not found. UE may trigger cellreselection (for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state if suitable SS block (or CSI-RS)is not found even after that time period.

Method 7:

FIG. 11 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 7 according to an embodiment of thedisclosure.

Referring to FIG. 11 , UE selects the SS block with highest signalquality for initial PRACH preamble transmission at operation 1101. Thesignal quality is measured over the resources of SS block carrying PSSand/or SSS and/or DMRS for PBCH. The signal quality can be RSRP or RSRQor RSSI. In an embodiment, the UE may select the SS block with highestsignal quality amongst all SS blocks transmitted by gNB. In anotherembodiment, the UE may select the SS block with highest signal qualityamongst all SS blocks for which measurements are available.

The UE then selects a PRACH preamble and/or a PRACH resource (or PRACHoccasion) corresponding to the selected SS block to transmit a PRACHpreamble (i.e., Msg1). The UE determines whether contention free PRACHpreambles and/or resources are configured for the selected SS block atoperation 1102. If the UE is configured with a contention free (i.e.,dedicated) PRACH preamble and/or PRACH resource corresponding to theselected SS block, the UE selects a dedicated PRACH preamble and/orPRACH resource corresponding to the selected block at operation 1103.Otherwise, the UE selects PRACH preamble and/or PRACH resourcecorresponding to the selected SS block from contention based subset ofPRACH preambles and/or PRACH resources corresponding to the selected SSblock at operation 1104.

If SS block is associated with a dedicated preamble the UE uses thatPRACH preamble. Otherwise, the UE selects a PRACH preamble randomly fromthe contention based PRACH preambles corresponding to the selected SSblock.

If SS block is associated with dedicated PRACH resources (PRACHoccasions), the UE selects a PRACH resource (PRACH occasion) fromdedicated PRACH resources otherwise the UE selects a PRACH resource(PRACH occasion) from contention based PRACH resources (PRACH occasions)corresponding to the selected SS block. The UE may select the earliestavailable PRACH resource (PRACH occasion) (dedicated if availableotherwise contention) of PRACH resources (PRACH occasions) correspondingto the selected SS block. In an embodiment, the UE may select randomlyone PRACH resource (or PRACH occasion) from configured PRACH resources(or PRACH occasions) (dedicated if available otherwise contention)corresponding to the selected SS block. In case multiple frequencydivision multiplexed PRACH resources (PRACH occasions) are available intime corresponding to the selected SS block, the UE randomly selectswith equal probability one PRACH resource (PRACH occasion) fromavailable multiple frequency division multiplexed PRACH resources (PRACHoccasions). The UE randomly selects with equal probability a PRACHpreamble from configured set of PRACH preambles.

The UE transmits Msg1 using the selected PRACH preamble and/or PRACHresource corresponding to the selected SS block at operation 1105.

For calculating the power for transmitting the PRACH, the UE estimatesthe path loss based on signals received in the selected SS block. Aftertransmitting the Msg1, the UE determines whether a RAR (i.e., Msg2)corresponding to Msg1 transmission is successfully received at operation1106. If the UE successfully receives the RAR, there is no need toretransmit Msg1 at operation 1107. If the UE is not able to receive theRAR, the UE determines whether the UE has performed maximum number ofallowed Msg1 transmissions at operation 1108. The UE retransmits theMsg1 if the UE has not yet transmitted maximum number of allowed Msg1transmissions. If the UE has performed maximum number of allowed Msg1transmissions, the UE does not retransmit Msg1. During theretransmission, the UE does not reselect the SS block. The UE uses thesame SS block as selected for initial transmission. SS block is selectedwhen random access procedure is initiated and the same SS block is usedfor PRACH preamble and/or PRACH resource (or PRACH occasion) selectionand path loss estimation for all (re-)transmissions of Msg1 during arandom access procedure. In an alternate embodiment, duringretransmission UE may select the SS block in same manner as initialtransmission.

In an alternate embodiment of this method, instead of SS block, CSI-RScan be used. UE selects CSI-RS instead of SS block using same procedureas explained above for SS block. The UE may select PRACH preamble and/orPRACH resource (or PRACH occasion) from PRACH preambles and/or PRACHresources (or PRACH occasion) corresponding to the selected CSI-RS.

Key Point:

UE may select SS block (or CSI-RS) with highest signal quality. Same SSblock (or CSI-RS) is used for Msg1 (re-) transmission during a randomaccess procedure. UE may select PRACH preamble and/or PRACH resourcecorresponding to the selected SS block (or CSI-RS) from CF resources (ifconfigured); otherwise UE may select PRACH preamble and/or PRACHresource corresponding to the selected SS block from CB resources.

Method 8:

FIG. 12 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 8 according to an embodiment of thedisclosure.

Referring to FIG. 12 , UE selects the SS block with highest signalquality for initial PRACH preamble transmission at operation 1201. Thesignal quality is measured over the resources of SS block carrying PSSand/or SSS and/or DMRS for PBCH. The signal quality can be RSRP or RSRQor RSSI. In this method, the UE may select the SS block with highestsignal quality amongst the SS blocks for which contention free preambleand/or resources are configured to UE by gNB.

The UE then selects a PRACH preamble and/or a PRACH resource (or PRACHoccasion) corresponding to the selected SS block at operation 1202, andthe UE transmits Msg1 using the selected PRACH preamble and/or PRACHresource corresponding to the selected SS block at operation 1203.

If SS block is associated with a dedicated preamble the UE uses thatPRACH preamble. Otherwise, the UE selects a PRACH preamble randomly fromthe contention based PRACH preambles corresponding to the selected SSblock.

If SS block is associated with dedicated PRACH resources (PRACHoccasions), the UE selects a PRACH resource (PRACH occasion) fromdedicated PRACH resources otherwise the UE selects a PRACH resource(PRACH occasion) from contention based PRACH resources (PRACH occasions)corresponding to the selected SS block. The UE may select the earliestavailable PRACH resource (PRACH occasion) (dedicated if availableotherwise contention) of PRACH resources (PRACH occasions) correspondingto the selected SS block. In an embodiment, the UE may select randomlyone PRACH resource (or PRACH occasion) from configured PRACH resources(or PRACH occasions) (dedicated if available otherwise contention)corresponding to the selected SS block. In case multiple frequencydivision multiplexed PRACH resources (PRACH occasions) are available intime corresponding to the selected SS block, the UE randomly selectswith equal probability one PRACH resource (PRACH occasion) fromavailable multiple frequency division multiplexed PRACH resources (PRACHoccasions). The UE randomly selects with equal probability a PRACHpreamble from configured set of PRACH preambles.

For calculating the power for transmitting the PRACH, the UE estimatesthe path loss based on signals received in the selected SS block. Aftertransmitting the Msg1, the UE determines whether a RAR (i.e., Msg2)corresponding to Msg1 transmission is successfully received at operation1204. If the UE successfully receives the RAR, there is no need toretransmit Msg1 at operation 1205. If the UE is not able to receive theRAR, the UE determines whether the UE has performed maximum number ofallowed Msg1 transmissions at operation 1206. The UE retransmits theMsg1 if the UE has not yet transmitted maximum number of allowed Msg1transmissions. If the UE has performed maximum number of allowed Msg1transmissions, the UE does not retransmit Msg1. During theretransmission, the UE does not reselect the SS block. The UE uses thesame SS block as selected for initial transmission. SS block is selectedwhen random access procedure is initiated and the same SS block is usedfor PRACH preamble and/or PRACH resource (or PRACH occasion) selectionand path loss estimation for all (re-)transmissions of Msg1 during arandom access procedure. In an alternate embodiment, duringretransmission UE may select the SS block in same manner as initialtransmission.

In an alternate embodiment of this method, instead of SS block, CSI-RScan be used. UE selects CSI-RS instead of SS block using same procedureas explained above for SS block. The UE may select PRACH preamble and/orPRACH resource (or PRACH occasion) from PRACH preambles and/or PRACHresources (or PRACH occasion) corresponding to the selected CSI-RS.

Key Point:

UE may select SS block (or CSI-RS) with highest signal quality amongstthe SS blocks (or CSI-RSs) for which contention free preamble and/orresource is provided to UE. Same SS block (or CSI-RS) is used for Msg1(re-) transmission during a random access procedure. UE may select atleast one of PRACH preamble and/or PRACH resource corresponding to theselected SS block (or CSI-RS) from CF resources.

Method 9:

FIG. 13 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 9 according to an embodiment of thedisclosure.

Referring to FIG. 13 , UE selects a suitable SS block for initial PRACHpreamble transmission at operation 1301. A SS block is suitable ifsignal quality of SS block is greater than the threshold‘SSBlockThreshold’. In an embodiment, a SS block is suitable if signalquality of SS block is greater than or equal to a threshold‘SSBlockThreshold’. The SSBlockThreshold can be configured by network insystem information (e.g., together with PRACH configuration or in RMSI)or handover command or in dedicated RRC signaling. The signal quality ismeasured over the resources of SS block carrying PSS and/or SSS and/orDMRS for PBCH. The signal quality can be RSRP or RSRQ or RSSI. In casemultiple SS blocks are suitable, the UE may select a SS block in one ofthe following ways:

UE may select the SS block with highest signal quality amongst thesuitable SS blocks.

UE may select the SS block corresponding to which RACH resource (orPRACH occasion) is available earliest in time amongst the suitable SSblocks.

UE may select randomly with equal probability one of the SS blockamongst the suitable SS blocks.

UE may select any SS block amongst the suitable SS blocks.

UE may select one of the following methods based on indication (can besignaled as part of PRACH configuration in SI and/or handover commandand/or in dedicated RRC signaling) from network: select the SS blockwith highest signal quality amongst the suitable SS blocks or select theSS block corresponding to which RACH resource (or PRACH occasion) isavailable earliest in time amongst the suitable SS blocks or selectrandomly with equal probability one of the SS block amongst the suitableSS blocks.

The UE then selects a PRACH preamble and/or a PRACH resource (or PRACHoccasion) corresponding to the selected SS block to transmit a PRACHpreamble (i.e., Msg1). The UE determines whether contention free PRACHpreambles and/or resources are configured for the selected SS block atoperation 1302. If the UE is configured with contention free (i.e.,dedicated) PRACH preamble and/or PRACH resource corresponding to theselected SS block, the UE selects dedicated PRACH preamble and/or PRACHresource corresponding to the selected block at operation 1303.Otherwise, the UE selects PRACH preamble and/or PRACH resourcecorresponding to the selected SS block from contention based subset ofPRACH preambles and/or PRACH resources corresponding to the selected SSblock at operation 1304.

If SS block is associated with a dedicated preamble the UE uses thatPRACH preamble. Otherwise, the UE selects a PRACH preamble randomly fromthe contention based PRACH preambles corresponding to the selected SSblock.

If SS block is associated with dedicated PRACH resources (PRACHoccasions), the UE selects a PRACH resource (PRACH occasion) fromdedicated PRACH resources otherwise the UE selects a PRACH resource(PRACH occasion) from contention based PRACH resources (PRACH occasions)corresponding to the selected SS block. The UE may select the earliestavailable PRACH resource (PRACH occasion) (dedicated if availableotherwise contention) of PRACH resources (PRACH occasions) correspondingto the selected SS block. In an embodiment, the UE may select randomlyone PRACH resource (or PRACH occasion) from configured PRACH resources(or PRACH occasions) (dedicated if available otherwise contention)corresponding to the selected SS block. In case multiple frequencydivision multiplexed PRACH resources (PRACH occasions) are available intime corresponding to the selected SS block, the UE randomly selectswith equal probability one PRACH resource (PRACH occasion) fromavailable multiple frequency division multiplexed PRACH resources (PRACHoccasions). The UE randomly selects with equal probability a PRACHpreamble from configured set of PRACH preambles.

The UE transmits Msg1 using the selected PRACH preamble and/or PRACHresource corresponding to the selected SS block at operation 1305.

For calculating the power for transmitting the PRACH, the UE estimatesthe path loss based on signals received in the selected SS block. Aftertransmitting the Msg1, the UE determines whether a RAR (i.e., Msg2)corresponding to Msg1 transmission is successfully received at operation1306. If the UE successfully receives the RAR, there is no need toretransmit Msg1 at operation 1307. If the UE is not able to receive theRAR, the UE determines whether the UE has performed maximum number ofallowed Msg1 transmissions at operation 1308. The UE retransmits theMsg1 if the UE has not yet transmitted maximum number of allowed Msg1transmissions. If the UE has performed maximum number of allowed Msg1transmissions, the UE does not retransmit Msg1. During theretransmission, the UE does not reselect the SS block. The UE uses thesame SS block as selected for initial transmission. Suitable SS block isselected when random access procedure is initiated and the same SS blockis used for PRACH preamble and/or PRACH resource (or PRACH occasion)selection and path loss estimation for all (re-)transmissions of Msg1during a random access procedure. In case suitable SS block is notfound, the UE may reselect a suitable SS block during retransmission asexplained later.

In the procedure explained above, it is possible that the UE is not ableto find any suitable SS block. In this case the UE may perform one ofthe following:

The UE does not transmit Msg1. Additionally, the UE may trigger cellreselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state.

The UE selects SS block with highest signal quality among all the SSblocks or among the SS blocks for which measurements are available. Inthis case (i.e., when suitable SS block is not selected), duringretransmission of Msg1 the UE may change SS block if SS block forprevious transmission is still not suitable and another suitable SSblock is found. In an embodiment, the UE may be allowed to transmit Msg1without selecting a suitable SS block for ‘N’ number of times. ParameterN can be pre-defined or signaled by network.

The UE may delay Msg1 transmission until the UE founds suitable SSblock. In one embodiment, the UE may delay Msg1 transmission for amaximum time period ‘T’. The time period T can be configured by networkin system information (e.g., together with PRACH configuration or inRMSI) or handover command or in dedicated RRC signaling. After expiry ofthis time if suitable SS block is still not found the UE may triggercell reselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state. Alternately, after expiry of thistime if suitable SS block is still not found, the UE may select SS blockwith highest signal quality among all the SS blocks or among the SSblocks for which measurements are available. In an alternate embodiment,during retransmission UE may select the SS block in same manner asinitial transmission.

In an alternate embodiment of this method, instead of SS block, CSI-RScan be used. UE selects CSI-RS instead of SS block using same procedureas explained above for SS block. The UE may select PRACH preamble and/orPRACH resource (or PRACH occasion) from PRACH preambles and/or PRACHresources (or PRACH occasion) corresponding to the selected CSI-RS.

Key Point:

1. UE may select suitable (signal quality>‘SSBlockThreshold’) SS block(or CSI-RS) when random access procedure is initiated. UE may use theselected SS block (or CSI-RS) for PRACH preamble and/or PRACH resource(or PRACH occasion) selection and path loss estimation for all(re-)transmissions of Msg1 during a random access procedure. Contentionfree PRACH preamble and/or PRACH resource for the selected SS block isselected if available. Otherwise contention based PRACH preamble and/orPRACH resource for the selected SS block is selected.

2. UE may select SS block (or CSI-RS) with highest signal quality ifsuitable SS block is not found.

3. UE may change the SS block (or CSI-RS) if suitable SS block (orCSI-RS) was not used for previous transmission and SS block (or CSI-RS)for previous transmission is still not suitable and another suitable SSblock (or CSI-RS) is found.

4. UE may reselect the cell if suitable SS block (or CSI-RS) is notfound.

5. UE may delay the Msg1 transmission until suitable SS block (orCSI-RS) is found.

6. UE may delay the Msg1 transmission for a defined time period ifsuitable SS block (or CSI-RS) is not found. UE may trigger cellreselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state if suitable SS block (or CSI-RS)is not found even after that time period.

Method 10:

FIG. 14 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 10 according to an embodiment of thedisclosure.

Referring to FIG. 14 , UE selects a suitable SS block for initial PRACHpreamble transmission at operation 1401. A SS block is suitable ifsignal quality of SS block is greater than the threshold‘SSBlockThreshold’. In an embodiment, a SS block is suitable if signalquality of SS block is greater than or equal to a threshold‘SSBlockThreshold’. The SSBlockThreshold can be configured by network insystem information (e.g., together with PRACH configuration or in RMSI)or handover command or in dedicated RRC signaling. The signal quality ismeasured over the resources of SS block carrying PSS and/or SSS and/orDMRS for PBCH. The signal quality can be RSRP or RSRQ or RSSI.

In this method the UE first check if there is a suitable SS blockamongst the SS blocks for which dedicated PRACH preambles and/or PRACHresources are configured at operation 1402. If a suitable SS block forwhich dedicated PRACH preambles and/or PRACH resources are configured isfound, the UE selects that SS block and selects a dedicated PRACHpreamble and/or PRACH resource corresponding to the selected SS block atoperation 1403. In case multiple SS blocks are suitable for which adedicated preamble and/or resource is configured, the UE may select a SSblock in one of the following ways:

UE may select the SS block with highest signal quality amongst thesuitable SS blocks.

UE may select the SS block corresponding to which RACH resource (orPRACH occasion) is available earliest in time amongst the suitable SSblocks.

UE may select randomly with equal probability one of the SS blockamongst the suitable SS blocks.

UE may select any SS block amongst the suitable SS blocks.

UE may select one of the following methods based on indication (can besignaled as part of PRACH configuration in SI and/or handover commandand/or in dedicated RRC signaling) from network: select the SS blockwith highest signal quality amongst the suitable SS blocks or select theSS block corresponding to which RACH resource (or PRACH occasion) isavailable earliest in time amongst the suitable SS blocks or selectrandomly with equal probability one of the SS block amongst the suitableSS blocks.

If a suitable SS block is not found, amongst the SS blocks for whichdedicated PRACH preambles and/or PRACH resources are configured, the UEselects a suitable block amongst the SS blocks for which contentionbased preambles and/or resources are configured at operation 1404, andthe UE selects a contention based PRACH preamble and/or PRACH resourcecorresponding to the selected SS block at operation 1405. In casemultiple SS blocks are suitable for which a contention based preambleand/or resource is configured, the UE may select a SS block in one ofthe following ways:

UE may select the SS block with highest signal quality amongst thesuitable SS blocks.

UE may select the SS block corresponding to which RACH resource (orPRACH occasion) is available earliest in time amongst the suitable SSblocks.

UE may select randomly with equal probability one of the SS blockamongst the suitable SS blocks.

UE may select any SS block amongst the suitable SS blocks.

UE may select one of the following methods based on indication (can besignaled as part of PRACH configuration in SI and/or handover commandand/or in dedicated RRC signaling) from network: select the SS blockwith highest signal quality amongst the suitable SS blocks or select theSS block corresponding to which RACH resource (or PRACH occasion) isavailable earliest in time amongst the suitable SS blocks or selectrandomly with equal probability one of the SS block amongst the suitableSS blocks.

The UE then transmits a PRACH preamble (i.e., Msg1) using the selectedPRACH preamble and/or PRACH resource corresponding to the selected SSblock at operation 1406.

If SS block is associated with a dedicated preamble the UE uses thatPRACH preamble. Otherwise, the UE selects a PRACH preamble randomly fromthe contention based PRACH preambles corresponding to the selected SSblock.

If SS block is associated with dedicated PRACH resources (PRACHoccasions), the UE selects a PRACH resource (PRACH occasion) fromdedicated PRACH resources otherwise the UE selects a PRACH resource(PRACH occasion) from contention based PRACH resources (PRACH occasions)corresponding to the selected SS block. The UE may select the earliestavailable PRACH resource (PRACH occasion) (dedicated if availableotherwise contention) of PRACH resources (PRACH occasions) correspondingto the selected SS block. In an embodiment, the UE may select randomlyone PRACH resource (or PRACH occasion) from configured PRACH resources(or PRACH occasions) (dedicated if available otherwise contention)corresponding to the selected SS block. In case multiple frequencydivision multiplexed PRACH resources (PRACH occasions) are available intime corresponding to the selected SS block, the UE randomly selectswith equal probability one PRACH resource (PRACH occasion) fromavailable multiple frequency division multiplexed PRACH resources (PRACHoccasions). The UE randomly selects with equal probability a PRACHpreamble from configured set of PRACH preambles.

For calculating the power for transmitting the PRACH, the UE estimatesthe path loss based on signals received in the selected SS block. Aftertransmitting the Msg1, the UE determines whether a RAR (i.e., Msg2)corresponding to Msg1 transmission is successfully received at operation1407. If the UE successfully receives the RAR, there is no need toretransmit Msg1 at operation 1408. If the UE is not able to receive theRAR, the UE determines whether the UE has performed maximum number ofallowed Msg1 transmissions at operation 1409. The UE retransmits theMsg1 if the UE has not yet transmitted maximum number of allowed Msg1transmissions. If the UE has performed maximum number of allowed Msg1transmissions, the UE does not retransmit Msg1. During theretransmission, the UE does not reselect the SS block. The UE uses thesame SS block as selected for initial transmission. Suitable SS block isselected when random access procedure is initiated and the same SS blockis used for PRACH preamble and/or PRACH resource (or PRACH occasion)selection and path loss estimation for all (re-)transmissions of Msg1during a random access procedure. In case suitable SS block is notfound, the UE may reselect a suitable SS block during retransmission asexplained later. In an alternate embodiment, during retransmission UEmay select the SS block in same manner as initial transmission.

In the procedure explained above, it is possible that the UE is not ableto find any suitable SS block while selecting SS block corresponding tocontention based preambles and/or resources. In this case the UE mayperform one of the following:

The UE does not transmit Msg1. Additionally, the UE may trigger cellreselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state.

The UE selects SS block with highest signal quality among all the SSblocks or among the SS blocks for which measurements are available. Inthis case (i.e., when suitable SS block is not selected), duringretransmission of Msg1 the UE may change SS block if SS block forprevious transmission is still not suitable and another suitable SSblock is found. In an embodiment, the UE may be allowed to transmit Msg1without selecting a suitable SS block for ‘N’ number of times. ParameterN can be pre-defined or signaled by network.

The UE may delay Msg1 transmission until the UE founds suitable SSblock. In one embodiment, the UE may delay Msg1 transmission for amaximum time period ‘T’. The time period T can be configured by networkin system information (e.g., together with PRACH configuration or inRMSI) or handover command or in dedicated RRC signaling. After expiry ofthis time if suitable SS block is still not found the UE may triggercell reselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state. Alternately, after expiry of thistime if suitable SS block is still not found, the UE may select SS blockwith highest signal quality among all the SS blocks or among the SSblocks for which measurements are available.

In an alternate embodiment of this method, instead of SS block, CSI-RScan be used. UE selects CSI-RS instead of SS block using same procedureas explained above for SS block. The UE may select PRACH preamble and/orPRACH resource (or PRACH occasion) from PRACH preambles and/or PRACHresources (or PRACH occasion) corresponding to the selected CSI-RS.

Key Point:

1. UE may select suitable SS block (or CSI-RS) from SS blocks (orCSI-RSs) for which CF resources are configured. If no suitable SS block(or CSI-RS) is found from SS blocks (or CSI-RSs) for which CF resourcesare configured, UE may select suitable SS block (or CSI-RS) from SSblocks (or CSI-RSs) for which CB resources are configured. UE may usethe selected SS block (or CSI-RS) for PRACH preamble and/or PRACHresource (or PRACH occasion) selection and path loss estimation for all(re-)transmissions of Msg1 during a random access procedure.

2. UE may select SS block (or CSI-RS) with highest signal quality ifsuitable SS block is not found.

3. UE may change the SS block (or CSI-RS) if suitable SS block (orCSI-RS) was not used for previous transmission and SS block (or CSI-RS)for previous transmission is still not suitable and another suitable SSblock (or CSI-RS) is found.

4. UE may reselect the cell if suitable SS block (or CSI-RS) is notfound.

5. UE may delay the Msg1 transmission until suitable SS block (orCSI-RS) is found.

6. UE may delay the Msg1 transmission for a defined time period ifsuitable SS block (or CSI-RS) is not found. UE may trigger cellreselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state if suitable SS block (or CSI-RS)is not found even after that time period.

Method 11:

FIG. 15 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 11 according to an embodiment of thedisclosure.

Referring to FIG. 15 , UE selects a suitable SS block for initial PRACHpreamble transmission at operation 1501. A SS block is suitable ifsignal quality of SS block is greater than the threshold‘SSBlockThreshold’. In an embodiment, a SS block is suitable if signalquality of SS block is greater than or equal to a threshold‘SSBlockThreshold’. The SSBlockThreshold can be configured by network insystem information (e.g., together with PRACH configuration or in RMSI)or handover command or in dedicated RRC signaling. The signal quality ismeasured over the resources of SS block carrying PSS and/or SSS and/orDMRS for PBCH. The signal quality can be RSRP or RSRQ or RSSI.

In this method the UE first check if there is a suitable SS blockamongst the SS blocks for which dedicated PRACH preambles and/or PRACHresources are configured at operation 1502. If a suitable SS block forwhich dedicated PRACH preambles and/or PRACH resources are configured isfound, the UE selects that SS block and selects a dedicated PRACHpreamble and/or PRACH resource corresponding to the selected SS block atoperation 1504. In case multiple SS blocks are suitable for which adedicated preamble and/or resource is configured, the UE may select a SSblock in one of the following ways:

UE may select the SS block with highest signal quality amongst thesuitable SS blocks.

UE may select the SS block corresponding to which RACH resource (orPRACH occasion) is available earliest in time amongst the suitable SSblocks.

UE may select randomly with equal probability one of the SS blockamongst the suitable SS blocks.

UE may select any SS block amongst the suitable SS blocks.

UE may select one of the following methods based on indication (can besignaled as part of PRACH configuration in SI and/or handover commandand/or in dedicated RRC signaling) from network: select the SS blockwith highest signal quality amongst the suitable SS blocks or select theSS block corresponding to which RACH resource (or PRACH occasion) isavailable earliest in time amongst the suitable SS blocks or selectrandomly with equal probability one of the SS block amongst the suitableSS blocks.

If a suitable SS block is not found, amongst the SS blocks for whichdedicated PRACH preambles and/or PRACH resources are configured, the UEselects a SS block with highest signal quality amongst the SS blocks forwhich dedicated PRACH preambles and/or PRACH resources are configured atoperation 1503, and a dedicated PRACH preamble and/or PRACH resourcecorresponding to the selected SS block at operation 1504.

The UE then transmits a PRACH preamble (i.e., Msg1) using the selectedPRACH preamble and/or PRACH resource corresponding to the selected SSblock at operation 1505.

If SS block is associated with a dedicated preamble the UE uses thatPRACH preamble. Otherwise, the UE selects a PRACH preamble randomly fromthe contention based PRACH preambles corresponding to the selected SSblock.

If SS block is associated with dedicated PRACH resources (PRACHoccasions), the UE selects a PRACH resource (PRACH occasion) fromdedicated PRACH resources otherwise the UE selects a PRACH resource(PRACH occasion) from contention based PRACH resources (PRACH occasions)corresponding to the selected SS block. The UE may select the earliestavailable PRACH resource (PRACH occasion) (dedicated if availableotherwise contention) of PRACH resources (PRACH occasions) correspondingto the selected SS block. In an embodiment, the UE may select randomlyone PRACH resource (or PRACH occasion) from configured PRACH resources(or PRACH occasions) (dedicated if available otherwise contention)corresponding to the selected SS block. In case multiple frequencydivision multiplexed PRACH resources (PRACH occasions) are available intime corresponding to the selected SS block, the UE randomly selectswith equal probability one PRACH resource (PRACH occasion) fromavailable multiple frequency division multiplexed PRACH resources (PRACHoccasions). The UE randomly selects with equal probability a PRACHpreamble from configured set of PRACH preambles.

For calculating the power for transmitting the PRACH, the UE estimatesthe path loss based on signals received in the selected SS block. Aftertransmitting the Msg1, the UE determines whether a RAR (i.e., Msg2)corresponding to Msg1 transmission is successfully received at operation1506. If the UE successfully receives the RAR, there is no need toretransmit Msg1 at operation 1507. If UE is not able to receive the RAR,the UE determines whether the UE has performed maximum number of allowedMsg1 transmissions at operation 1508. The UE retransmits the Msg1 if theUE has not yet transmitted maximum number of allowed Msg1 transmissions.If the UE has performed maximum number of allowed Msg1 transmissions,the UE does not retransmit Msg1. During the retransmission, the UE doesnot reselect the SS block. The UE uses the same SS block as selected forinitial transmission. Suitable SS block is selected when random accessprocedure is initiated and the same SS block is used for PRACH preambleand/or PRACH resource (or PRACH occasion) selection and path lossestimation for all (re-)transmissions of Msg1 during a random accessprocedure. In an alternate embodiment, during retransmission UE mayselect the SS block in same manner as initial transmission.

In an alternate embodiment of this method, instead of SS block, CSI-RScan be used. UE selects CSI-RS instead of SS block using same procedureas explained above for SS block. The UE may select PRACH preamble and/orPRACH resource (or PRACH occasion) from PRACH preambles and/or PRACHresources (or PRACH occasion) corresponding to the selected CSI-RS.

Key Point:

UE may select suitable SS block (or CSI-RS) from SS blocks (or CSI-RSs)for which CF resources are configured. If no suitable SS block (orCSI-RS) is found from SS blocks (or CSI-RSs) for which CF resources areconfigured, UE may select SS block (or CSI-RS) with highest signalquality from SS blocks (or CSI-RSs) for which CF resources areconfigured. UE may use the selected SS block (or CSI-RS) for PRACHpreamble and/or PRACH resource (or PRACH occasion) selection and pathloss estimation for all (re-)transmissions of Msg1 during a randomaccess procedure.

Method 12:

FIG. 16 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 12 according to an embodiment of thedisclosure.

Referring to FIG. 16 , UE selects the SS block with highest signalquality for initial PRACH preamble transmission at operation 1601. Thesignal quality is measured over the resources of SS block carrying PSSand/or SSS and/or DMRS for PBCH. The signal quality can be RSRP or RSRQor RSSI. In an embodiment, the UE may select the SS block with highestsignal quality amongst all SS blocks transmitted by gNB. In anotherembodiment, the UE may select the SS block with highest signal qualityamongst all SS blocks for which measurements are available.

The UE then selects a PRACH preamble and/or a PRACH resource (or PRACHoccasion) corresponding to the selected SS block to transmit a PRACHpreamble (i.e., Msg1). The UE determines whether contention free PRACHpreambles and/or resources are configured for the selected SS block atoperation 1602. If the UE is configured with a contention free (i.e.,dedicated) PRACH preamble and/or PRACH resource corresponding to theselected SS block, the UE selects a dedicated PRACH preamble and/orPRACH resource corresponding to the selected block at operation 1603.Otherwise, the UE selects PRACH preamble and/or PRACH resourcecorresponding to the selected SS block from contention based subset ofPRACH preambles and/or PRACH resources corresponding to the selected SSblock at operation 1604.

If SS block is associated with a dedicated preamble the UE uses thatPRACH preamble. Otherwise, the UE selects a PRACH preamble randomly fromthe contention based PRACH preambles corresponding to the selected SSblock.

If SS block is associated with dedicated PRACH resources (PRACHoccasions), the UE selects a PRACH resource (PRACH occasion) fromdedicated PRACH resources otherwise the UE selects a PRACH resource(PRACH occasion) from contention based PRACH resources (PRACH occasions)corresponding to the selected SS block. The UE may select the earliestavailable PRACH resource (PRACH occasion) (dedicated if availableotherwise contention) of PRACH resources (PRACH occasions) correspondingto the selected SS block. In an embodiment, the UE may select randomlyone PRACH resource (or PRACH occasion) from configured PRACH resources(or PRACH occasions) (dedicated if available otherwise contention)corresponding to the selected SS block. In case multiple frequencydivision multiplexed PRACH resources (PRACH occasions) are available intime corresponding to the selected SS block, the UE randomly selectswith equal probability one PRACH resource (PRACH occasion) fromavailable multiple frequency division multiplexed PRACH resources (PRACHoccasions). The UE randomly selects with equal probability a PRACHpreamble from configured set of PRACH preambles.

The UE transmits Msg1 using the selected PRACH preamble and/or PRACHresource corresponding to the selected SS block at operation 1605.

For calculating the power for transmitting the PRACH, the UE estimatesthe path loss based on signals received in the selected SS block. Aftertransmitting the Msg1, the UE determines whether a RAR (i.e., Msg2)corresponding to Msg1 transmission is successfully received at operation1606. If the UE successfully receives the RAR, there is no need toretransmit Msg1 at operation 1607. If the UE is not able to receive theRAR, the UE determines whether the UE has performed maximum number ofallowed Msg1 transmissions at operation 1608. The UE retransmits theMsg1 if the UE has not yet transmitted maximum number of allowed Msg1transmissions. If the UE has performed maximum number of allowed Msg1transmissions, the UE does not retransmit Msg1. During theretransmission, the UE determines whether signal quality of SS blockselected for previous Msg1 transmission is greater than or equal to athreshold ‘SSBlockThreshold’ at operation 1609. If the signal quality ofthe SS block selected for the previous Msg1 transmission is greater thanor equal to the threshold ‘SSBlockThreshold’ the UE does not reselectthe SS block. The threshold can be configured by network in systeminformation (e.g., together with PRACH configuration or in RMSI) orhandover command or in dedicated RRC signaling. The UE uses the same SSblock as selected for the previous transmission for PRACH preambleand/or PRACH resource selection and path loss estimation forretransmission (i.e., next Msg1 transmission). During theretransmission, if the signal quality of the SS block selected for theprevious Msg1 transmission is less than the threshold‘SSBlockThreshold’, the UE may reselect SS block at operation 1610. TheUE may select the SS block with highest signal quality amongst all SSblocks transmitted by gNB. In another embodiment, the UE may select theSS block with highest signal quality amongst all SS blocks for whichmeasurements are available. In an alternate embodiment, duringretransmission UE may select the SS block in same manner as initialtransmission.

In an alternate embodiment of this method, instead of SS block, CSI-RScan be used. UE selects CSI-RS instead of SS block using same procedureas explained above for SS block. The UE may select PRACH preamble and/orPRACH resource (or PRACH occasion) from PRACH preambles and/or PRACHresources (or PRACH occasion) corresponding to the selected CSI-RS.

Key Point:

1. UE may select SS block (or CSI-RS) with highest signal quality whenrandom access procedure is initiated. UE reselects SS block (or CSI-RS)during retransmission if SS block (or CSI-RS) of previous transmissionis below a threshold based on latest measurement wherein SS block (orCSI-RS) with highest signal quality is selected during retransmission.UE may use the selected SS block (or CSI-RS) for PRACH preamble and/orPRACH resource (or PRACH occasion) selection and path loss estimationfor transmission of Msg1 during a random access procedure.

2. UE may select PRACH preamble and/or PRACH resource corresponding toselected SS block (or CSI-RS) from CF resources (if configured);otherwise UE may select PRACH preamble and/or PRACH resourcecorresponding to the selected SS block from CB resources.

Method 13:

FIG. 17 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 13 according to an embodiment of thedisclosure.

Referring to FIG. 17 , UE selects the SS block with highest signalquality for initial PRACH preamble transmission at operation 1701. Thesignal quality is measured over the resources of SS block carrying PSSand/or SSS and/or DMRS for PBCH. The signal quality can be RSRP or RSRQor RSSI. In an embodiment, the UE may select the SS block with highestsignal quality amongst all SS blocks transmitted by gNB. In anotherembodiment, the UE may select the SS block with highest signal qualityamongst all SS blocks for which measurements are available.

The UE then selects a PRACH preamble and/or a PRACH resource (or PRACHoccasion) corresponding to the selected SS block to transmit a PRACHpreamble (i.e., Msg1). The UE determines whether contention free PRACHpreambles and/or resources are configured for the selected SS block atoperation 1702. If the UE is configured with a contention free (i.e.,dedicated) PRACH preamble and/or PRACH resource corresponding to theselected SS block, the UE selects a dedicated PRACH preamble and/orPRACH resource corresponding to the selected block at operation 1703.Otherwise, the UE selects PRACH preamble and/or PRACH resourcecorresponding to the selected SS block from contention based subset ofPRACH preambles and/or PRACH resources corresponding to the selected SSblock at operation 1704.

If SS block is associated with a dedicated preamble the UE uses thatPRACH preamble. Otherwise, the UE selects a PRACH preamble randomly fromthe contention based PRACH preambles corresponding to the selected SSblock.

If SS block is associated with dedicated PRACH resources (PRACHoccasions), the UE selects a PRACH resource (PRACH occasion) fromdedicated PRACH resources otherwise the UE selects a PRACH resource(PRACH occasion) from contention based PRACH resources (PRACH occasions)corresponding to the selected SS block. The UE may select the earliestavailable PRACH resource (PRACH occasion) (dedicated if availableotherwise contention) of PRACH resources (PRACH occasions) correspondingto the selected SS block. In an embodiment, the UE may select randomlyone PRACH resource (or PRACH occasion) from configured PRACH resources(or PRACH occasions) (dedicated if available otherwise contention)corresponding to the selected SS block. In case multiple frequencydivision multiplexed PRACH resources (PRACH occasions) are available intime corresponding to the selected SS block, the UE randomly selectswith equal probability one PRACH resource (PRACH occasion) fromavailable multiple frequency division multiplexed PRACH resources (PRACHoccasions). The UE randomly selects with equal probability a PRACHpreamble from configured set of PRACH preambles.

The UE transmits Msg1 using the selected PRACH preamble and/or PRACHresource corresponding to the selected SS block at operation 1705.

For calculating the power for transmitting the PRACH, the UE estimatesthe path loss based on signals received in the selected SS block. Aftertransmitting the Msg1, the UE determines whether a RAR (i.e., Msg2)corresponding to Msg1 transmission is successfully received at operation1706. If the UE successfully receives the RAR, there is no need toretransmit Msg1 at operation 1707. If the UE is not able to receive theRAR, the UE determines whether the UE has performed maximum number ofallowed Msg1 transmissions at operation 1708. The UE retransmits theMsg1 if the UE has not yet transmitted maximum number of allowed Msg1transmissions. If the UE has performed maximum number of allowed Msg1transmissions, the UE does not retransmit Msg1. During theretransmission, the UE determines whether signal quality of SS blockselected for previous Msg1 transmission has still the highest signalingquality based on latest measurements at operation 1709. If the signalquality of the SS block selected for the previous Msg1 transmission hasthe highest signaling quality, the UE does not reselect the SS block.The threshold can be configured by network in system information (e.g.together with PRACH configuration or in RMSI) or handover command or indedicated RRC signaling. The UE uses the same SS block as selected forthe previous transmission for PRACH preamble and/or PRACH resourceselection and path loss estimation for retransmission (i.e., next Msg1transmission). During the retransmission, if the signal quality of theSS block selected for the previous Msg1 transmission does not havehighest signaling quality, the UE may reselect SS block at operation1710. The UE may select the SS block with highest signal quality amongstall SS blocks transmitted by gNB. In another embodiment, the UE mayselect the SS block with highest signal quality amongst all SS blocksfor which measurements are available. In an alternate embodiment, duringretransmission UE may select the SS block in same manner as initialtransmission.

In an alternate embodiment of this method, instead of SS block, CSI-RScan be used. UE selects CSI-RS instead of SS block using same procedureas explained above for SS block. The UE may select PRACH preamble and/orPRACH resource (or PRACH occasion) from PRACH preambles and/or PRACHresources (or PRACH occasion) corresponding to the selected CSI-RS.

Key Point:

1. UE may select SS block (or CSI-RS) with highest signal quality whenrandom access procedure is initiated. UE reselects SS block (or CSI-RS)during retransmission if SS block (or CSI-RS) of previous transmissiondoes not have the highest signal quality based on latest measurementwherein SS block (or CSI-RS) with highest signal quality is selectedduring retransmission. UE may use the selected SS block (or CSI-RS) forPRACH preamble and/or PRACH resource (or PRACH occasion) selection andpath loss estimation for transmission of Msg1 during a random accessprocedure.

2. UE may select PRACH preamble and/or PRACH resource corresponding toselected SS block (or CSI-RS) from CF resources (if configured);otherwise UE may select PRACH preamble and/or PRACH resourcecorresponding to the selected SS block from CB resources.

Method 14:

FIG. 18 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 14 according to an embodiment of thedisclosure.

Referring to FIG. 18 , UE selects the SS block with highest signalquality for initial PRACH preamble transmission at operation 1801. Thesignal quality is measured over the resources of SS block carrying PSSand/or SSS and/or DMRS for PBCH. The signal quality can be RSRP or RSRQor RSSI. In this method, the UE may select the SS block with highestsignal quality amongst the SS blocks for which contention free preambleand/or resources are configured to UE by gNB.

The UE then selects a PRACH preamble and/or a PRACH resource (or PRACHoccasion) corresponding to the selected SS block at operation 1802, andthe UE transmits Msg1 using the selected PRACH preamble and/or PRACHresource corresponding to the selected SS block at operation 1803.

If SS block is associated with a dedicated preamble the UE uses thatPRACH preamble. Otherwise, the UE selects a PRACH preamble randomly fromthe contention based PRACH preambles corresponding to the selected SSblock.

If SS block is associated with dedicated PRACH resources (PRACHoccasions), the UE selects a PRACH resource (PRACH occasion) fromdedicated PRACH resources otherwise the UE selects a PRACH resource(PRACH occasion) from contention based PRACH resources (PRACH occasions)corresponding to the selected SS block. The UE may select the earliestavailable PRACH resource (PRACH occasion) (dedicated if availableotherwise contention) of PRACH resources (PRACH occasions) correspondingto the selected SS block. In an embodiment, the UE may select randomlyone PRACH resource (or PRACH occasion) from configured PRACH resources(or PRACH occasions) (dedicated if available otherwise contention)corresponding to the selected SS block. In case multiple frequencydivision multiplexed PRACH resources (PRACH occasions) are available intime corresponding to the selected SS block, the UE randomly selectswith equal probability one PRACH resource (PRACH occasion) fromavailable multiple frequency division multiplexed PRACH resources (PRACHoccasions). The UE randomly selects with equal probability a PRACHpreamble from configured set of PRACH preambles.

For calculating the power for transmitting the PRACH, the UE estimatesthe path loss based on signals received in the selected SS block. Aftertransmitting the Msg1, the UE determines whether a RAR (i.e., Msg2)corresponding to Msg1 transmission is successfully received at operation1804. If the UE successfully receives the RAR, there is no need toretransmit Msg1 at operation 1805. If the UE is not able to receive theRAR, the UE determines whether the UE has performed maximum number ofallowed Msg1 transmissions at operation 1806. The UE retransmits theMsg1 if the UE has not yet transmitted maximum number of allowed Msg1transmissions. If the UE has performed maximum number of allowed Msg1transmissions, the UE does not retransmit Msg1. During theretransmission, the UE determines whether signal quality of SS blockselected for previous Msg1 transmission is greater than or equal to athreshold ‘SSBlockThreshold’ at operation 1807. If the signal quality ofthe SS block selected for the previous Msg1 transmission is greater thanor equal to the threshold ‘SSBlockThreshold’ the UE does not reselectthe SS block. The threshold can be configured by network in systeminformation (e.g., together with PRACH configuration or in RMSI) orhandover command or in dedicated RRC signaling. The UE uses the same SSblock as selected for the previous transmission for PRACH preambleand/or PRACH resource selection and path loss estimation forretransmission (i.e., next Msg1 transmission). During theretransmission, if the signal quality of the SS block selected for theprevious Msg1 transmission is less than the threshold‘SSBlockThreshold’, the UE may reselect SS block at operation 1808. TheUE may select the SS block with highest signal quality amongst the SSblocks for which contention free preamble and/or resources areconfigured to UE by gNB.

In an alternate embodiment of this method, instead of SS block, CSI-RScan be used. UE selects CSI-RS instead of SS block using same procedureas explained above for SS block. The UE may select PRACH preamble and/orPRACH resource (or PRACH occasion) from PRACH preambles and/or PRACHresources (or PRACH occasion) corresponding to the selected CSI-RS.

Method 15:

FIG. 19 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 15 according to an embodiment of thedisclosure.

Referring to FIG. 19 , UE selects a suitable SS block for initial PRACHpreamble transmission at operation 1901. A SS block is suitable ifsignal quality of SS block is greater than the threshold‘SSBlockThreshold’. In an embodiment, a SS block is suitable if signalquality of SS block is greater than or equal to a threshold‘SSBlockThreshold’. The SSBlockThreshold can be configured by network insystem information (e.g., together with PRACH configuration or in RMSI)or handover command or in dedicated RRC signaling. The signal quality ismeasured over the resources of SS block carrying PSS and/or SSS and/orDMRS for PBCH. The signal quality can be RSRP or RSRQ or RSSI. In casemultiple SS blocks are suitable, the UE may select a SS block in one ofthe following ways:

UE may select the SS block with highest signal quality amongst thesuitable SS blocks.

UE may select the SS block corresponding to which RACH resource (orPRACH occasion) is available earliest in time amongst the suitable SSblocks.

UE may select randomly with equal probability one of the SS blockamongst the suitable SS blocks.

UE may select any SS block amongst the suitable SS blocks.

UE may select one of the following methods based on indication (can besignaled as part of PRACH configuration in SI and/or handover commandand/or in dedicated RRC signaling) from network: select the SS blockwith highest signal quality amongst the suitable SS blocks or select theSS block corresponding to which RACH resource (or PRACH occasion) isavailable earliest in time amongst the suitable SS blocks or selectrandomly with equal probability one of the SS block amongst the suitableSS blocks.

The UE then selects a PRACH preamble and/or a PRACH resource (or PRACHoccasion) corresponding to the selected SS block to transmit a PRACHpreamble (i.e., Msg1). The UE determines whether contention free PRACHpreambles and/or resources are configured for the selected SS block atoperation 1902. If the UE is configured with contention free (i.e.,dedicated) PRACH preamble and/or PRACH resource corresponding to theselected SS block, the UE selects dedicated PRACH preamble and/or PRACHresource corresponding to the selected block at operation 1903.Otherwise, the UE selects PRACH preamble and/or PRACH resourcecorresponding to the selected SS block from contention based subset ofPRACH preambles and/or PRACH resources corresponding to the selected SSblock at operation 1904.

If SS block is associated with a dedicated preamble the UE uses thatPRACH preamble. Otherwise, the UE selects a PRACH preamble randomly fromthe contention based PRACH preambles corresponding to the selected SSblock.

If SS block is associated with dedicated PRACH resources (PRACHoccasions), the UE selects a PRACH resource (PRACH occasion) fromdedicated PRACH resources otherwise the UE selects a PRACH resource(PRACH occasion) from contention based PRACH resources (PRACH occasions)corresponding to the selected SS block. The UE may select the earliestavailable PRACH resource (PRACH occasion) (dedicated if availableotherwise contention) of PRACH resources (PRACH occasions) correspondingto the selected SS block. In an embodiment, the UE may select randomlyone PRACH resource (or PRACH occasion) from configured PRACH resources(or PRACH occasions) (dedicated if available otherwise contention)corresponding to the selected SS block. In case multiple frequencydivision multiplexed PRACH resources (PRACH occasions) are available intime corresponding to the selected SS block, the UE randomly selectswith equal probability one PRACH resource (PRACH occasion) fromavailable multiple frequency division multiplexed PRACH resources (PRACHoccasions). The UE randomly selects with equal probability a PRACHpreamble from configured set of PRACH preambles.

The UE transmits Msg1 using the selected PRACH preamble and/or PRACHresource corresponding to the selected SS block at operation 1905.

For calculating the power for transmitting the PRACH, the UE estimatesthe path loss based on signals received in the selected SS block. Aftertransmitting the Msg1, the UE determines whether a RAR (i.e., Msg2)corresponding to Msg1 transmission is successfully received at operation1906. If the UE successfully receives the RAR, there is no need toretransmit Msg1 at operation 1907. If the UE is not able to receive theRAR, the UE determines whether the UE has performed maximum number ofallowed Msg1 transmissions at operation 1908. The UE retransmits theMsg1 if the UE has not yet transmitted maximum number of allowed Msg1transmissions. If the UE has performed maximum number of allowed Msg1transmissions, the UE does not retransmit Msg1. During theretransmission, the UE determines whether signal quality of the SS blockselected for the previous Msg1 transmission is greater than or equal toa threshold ‘SSBlockThreshold’ at operation 1909. If the signal qualityof the SS block selected for the previous Msg1 transmission is greaterthan equal to a threshold ‘SSBlockThreshold’, the UE does not reselectthe SS block. The threshold can be configured by network in systeminformation (e.g., together with PRACH configuration or in RMSI) orhandover command or in dedicated RRC signaling. The UE uses the same SSblock as selected for the previous transmission for PRACH preambleand/or PRACH resource selection and path loss estimation forretransmission (i.e., next Msg1 transmission). During theretransmission, if the signal quality of the SS block selected for theprevious Msg1 transmission is less than the threshold‘SSBlockThreshold’, the UE may reselect SS block at operation 1910. TheUE may select a suitable SS block. In case suitable SS block is notfound, the UE may reselect a suitable SS block during retransmission asexplained later.

In the procedure explained above, it is possible that the UE is not ableto find any suitable SS block. In this case the UE may perform one ofthe following:

The UE does not transmit Msg1. Additionally, the UE may trigger cellreselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state.

The UE selects SS block with highest signal quality among all the SSblocks or among the SS blocks for which measurements are available. Inthis case (i.e., when suitable SS block is not selected), duringretransmission of Msg1 the UE may change SS block if SS block forprevious transmission is still not suitable and another suitable SSblock is found. In an embodiment, the UE may be allowed to transmit Msg1without selecting a suitable SS block for ‘N’ number of times. ParameterN can be pre-defined or signaled by network.

The UE may delay Msg1 transmission until the UE founds suitable SSblock. In one embodiment, the UE may delay Msg1 transmission for amaximum time period ‘T’. The time period T can be configured by networkin system information (e.g., together with PRACH configuration or inRMSI) or handover command or in dedicated RRC signaling. After expiry ofthis time if suitable SS block is still not found the UE may triggercell reselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state. Alternately, after expiry of thistime if suitable SS block is still not found, the UE may select SS blockwith highest signal quality among all the SS blocks or among the SSblocks for which measurements are available.

In an alternate embodiment of this method, instead of SS block, CSI-RScan be used. UE selects CSI-RS instead of SS block using same procedureas explained above for SS block. The UE may select PRACH preamble and/orPRACH resource (or PRACH occasion) from PRACH preambles and/or PRACHresources (or PRACH occasion) corresponding to the selected CSI-RS.

Method 16:

FIG. 20 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 16 according to an embodiment of thedisclosure.

Referring to FIG. 20 , UE selects a suitable SS block for initial PRACHpreamble transmission at operation 2001. A SS block is suitable ifsignal quality of SS block is greater than the threshold‘SSBlockThreshold’. In an embodiment, a SS block is suitable if signalquality of SS block is greater than or equal to a threshold‘SSBlockThreshold’. The SSBlockThreshold can be configured by network insystem information (e.g., together with PRACH configuration or in RMSI)or handover command or in dedicated RRC signaling. The signal quality ismeasured over the resources of SS block carrying PSS and/or SSS and/orDMRS for PBCH. The signal quality can be RSRP or RSRQ or RSSI.

In this method the UE first check if there is a suitable SS blockamongst the SS blocks for which dedicated PRACH preambles and/or PRACHresources are configured at operation 2002. If a suitable SS block forwhich dedicated PRACH preambles and/or PRACH resources are configured isfound, the UE selects that SS block and selects a dedicated PRACHpreamble and/or PRACH resource corresponding to the selected SS block atoperation 2003. In case multiple SS blocks are suitable for which adedicated preamble and/or resource is configured, the UE may select a SSblock in one of the following ways:

UE may select the SS block with highest signal quality amongst thesuitable SS blocks.

UE may select the SS block corresponding to which RACH resource (orPRACH occasion) is available earliest in time amongst the suitable SSblocks.

UE may select randomly with equal probability one of the SS blockamongst the suitable SS blocks.

UE may select any SS block amongst the suitable SS blocks.

UE may select one of the following methods based on indication (can besignaled as part of PRACH configuration in SI and/or handover commandand/or in dedicated RRC signaling) from network: select the SS blockwith highest signal quality amongst the suitable SS blocks or select theSS block corresponding to which RACH resource (or PRACH occasion) isavailable earliest in time amongst the suitable SS blocks or selectrandomly with equal probability one of the SS block amongst the suitableSS blocks.

If a suitable SS block is not found, amongst the SS blocks for whichdedicated PRACH preambles and/or PRACH resources are configured, the UEselects a suitable block amongst the SS blocks for which contentionbased preambles and/or resources are configured at operation 2004, andthe UE selects a contention based PRACH preamble and/or PRACH resourcecorresponding to the selected SS block at operation 2005. In casemultiple SS blocks are suitable for which a contention based preambleand/or resource is configured, the UE may select a SS block in one ofthe following ways:

UE may select the SS block with highest signal quality amongst thesuitable SS blocks.

UE may select the SS block corresponding to which RACH resource (orPRACH occasion) is available earliest in time amongst the suitable SSblocks.

UE may select randomly with equal probability one of the SS blockamongst the suitable SS blocks.

UE may select any SS block amongst the suitable SS blocks.

UE may select one of the following methods based on indication (can besignaled as part of PRACH configuration in SI and/or handover commandand/or in dedicated RRC signaling) from network: select the SS blockwith highest signal quality amongst the suitable SS blocks or select theSS block corresponding to which RACH resource (or PRACH occasion) isavailable earliest in time amongst the suitable SS blocks or selectrandomly with equal probability one of the SS block amongst the suitableSS blocks.

The UE then transmits a PRACH preamble (i.e., Msg1) using the selectedPRACH preamble and/or PRACH resource corresponding to the selected SSblock at operation 2006.

If SS block is associated with a dedicated preamble the UE uses thatPRACH preamble. Otherwise, the UE selects a PRACH preamble randomly fromthe contention based PRACH preambles corresponding to the selected SSblock.

If SS block is associated with dedicated PRACH resources (PRACHoccasions), the UE selects a PRACH resource (PRACH occasion) fromdedicated PRACH resources otherwise the UE selects a PRACH resource(PRACH occasion) from contention based PRACH resources (PRACH occasions)corresponding to the selected SS block. The UE may select the earliestavailable PRACH resource (PRACH occasion) (dedicated if availableotherwise contention) of PRACH resources (PRACH occasions) correspondingto the selected SS block. In an embodiment, the UE may select randomlyone PRACH resource (or PRACH occasion) from configured PRACH resources(or PRACH occasions) (dedicated if available otherwise contention)corresponding to the selected SS block. In case multiple frequencydivision multiplexed PRACH resources (PRACH occasions) are available intime corresponding to the selected SS block, the UE randomly selectswith equal probability one PRACH resource (PRACH occasion) fromavailable multiple frequency division multiplexed PRACH resources (PRACHoccasions). The UE randomly selects with equal probability a PRACHpreamble from configured set of PRACH preambles.

For calculating the power for transmitting the PRACH, the UE estimatesthe path loss based on signals received in the selected SS block. Aftertransmitting the Msg1, the UE determines whether a RAR (i.e., Msg2)corresponding to Msg1 transmission is successfully received at operation2007. If the UE successfully receives the RAR, there is no need toretransmit Msg1 at operation 2008. If the UE is not able to receive theRAR, the UE determines whether the UE has performed maximum number ofallowed Msg1 transmissions at operation 2009. The UE retransmits theMsg1 if the UE has not yet transmitted maximum number of allowed Msg1transmissions. If the UE has performed maximum number of allowed Msg1transmissions, the UE does not retransmit Msg1. During theretransmission, the UE determines whether signal quality of SS blockselected for previous Msg1 transmission is greater than or equal to athreshold ‘SSBlockThreshold’ at operation 2010. If the signal quality ofthe SS block selected for the previous Msg1 transmission is greater thanor equal to the threshold ‘SSBlockThreshold’ the UE does not reselectthe SS block. The threshold can be configured by network in systeminformation (e.g., together with PRACH configuration or in RMSI) orhandover command or in dedicated RRC signaling. The UE uses the same SSblock as selected for the previous transmission for PRACH preambleand/or PRACH resource selection and path loss estimation forretransmission (i.e., next Msg1 transmission). During theretransmission, if the signal quality of the SS block selected for theprevious Msg1 transmission is less than the threshold‘SSBlockThreshold’, the UE may reselect SS block at operation 2011. TheUE may select a suitable SS block. In case suitable SS block is notfound, the UE may reselect a suitable SS block during retransmission asexplained later.

In the procedure explained above, it is possible that the UE is not ableto find any suitable SS block. In this case the UE may perform one ofthe following:

The UE does not transmit Msg1. Additionally, the UE may trigger cellreselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state.

The UE selects SS block with highest signal quality among all the SSblocks or among the SS blocks for which measurements are available. Inthis case (i.e., when suitable SS block is not selected), duringretransmission of Msg1 the UE may change SS block if SS block forprevious transmission is still not suitable and another suitable SSblock is found. In an embodiment, the UE may be allowed to transmit Msg1without selecting a suitable SS block for ‘N’ number of times. ParameterN can be pre-defined or signaled by network.

The UE may delay Msg1 transmission until the UE founds suitable SSblock. In one embodiment, the UE may delay Msg1 transmission for amaximum time period ‘T’. The time period T can be configured by networkin system information (e.g., together with PRACH configuration or inRMSI) or handover command or in dedicated RRC signaling. After expiry ofthis time if suitable SS block is still not found the UE may triggercell reselection for idle/inactive state and RLF (i.e., connectionre-establishment) for connected state. Alternately, after expiry of thistime if suitable SS block is still not found, the UE may select SS blockwith highest signal quality among all the SS blocks or among the SSblocks for which measurements are available.

In an alternate embodiment of this method, instead of SS block, CSI-RScan be used. UE selects CSI-RS instead of SS block using same procedureas explained above for SS block. The UE may select PRACH preamble and/orPRACH resource (or PRACH occasion) from PRACH preambles and/or PRACHresources (or PRACH occasion) corresponding to the selected CSI-RS.

Method 17:

FIG. 21 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 17 according to an embodiment of thedisclosure.

Referring to FIG. 21 , UE selects a suitable SS block for initial PRACHpreamble transmission at operation 2101. A SS block is suitable ifsignal quality of SS block is greater than the threshold‘SSBlockThreshold’. In an embodiment, a SS block is suitable if signalquality of SS block is greater than or equal to a threshold‘SSBlockThreshold’. The SSBlockThreshold can be configured by network insystem information (e.g., together with PRACH configuration or in RMSI)or handover command or in dedicated RRC signaling. The signal quality ismeasured over the resources of SS block carrying PSS and/or SSS and/orDMRS for PBCH. The signal quality can be RSRP or RSRQ or RSSI.

In this method the UE first check if there is a suitable SS blockamongst the SS blocks for which dedicated PRACH preambles and/or PRACHresources are configured at operation 2102. If a suitable SS block forwhich dedicated PRACH preambles and/or PRACH resources are configured isfound, the UE selects that SS block and selects a dedicated PRACHpreamble and/or PRACH resource corresponding to the selected SS block atoperation 2103. In case multiple SS blocks are suitable for which adedicated preamble and/or resource is configured, the UE may select a SSblock in one of the following ways:

UE may select the SS block with highest signal quality amongst thesuitable SS blocks.

UE may select the SS block corresponding to which RACH resource (orPRACH occasion) is available earliest in time amongst the suitable SSblocks.

UE may select randomly with equal probability one of the SS blockamongst the suitable SS blocks.

UE may select any SS block amongst the suitable SS blocks.

UE may select one of the following methods based on indication (can besignaled as part of PRACH configuration in SI and/or handover commandand/or in dedicated RRC signaling) from network: select the SS blockwith highest signal quality amongst the suitable SS blocks or select theSS block corresponding to which RACH resource (or PRACH occasion) isavailable earliest in time amongst the suitable SS blocks or selectrandomly with equal probability one of the SS block amongst the suitableSS blocks.

If a suitable SS block is not found, amongst the SS blocks for whichdedicated PRACH preambles and/or PRACH resources are configured, the UEselects a SS block with highest signal quality amongst the SS blocks forwhich dedicated PRACH preambles and/or PRACH resources are configured atoperation 2103, and a dedicated PRACH preamble and/or PRACH resourcecorresponding to the selected SS block at operation 2104.

The UE then transmits a PRACH preamble (i.e., Msg1) using the selectedPRACH preamble and/or PRACH resource corresponding to the selected SSblock at operation 2105.

If SS block is associated with a dedicated preamble the UE uses thatPRACH preamble. Otherwise, the UE selects a PRACH preamble randomly fromthe contention based PRACH preambles corresponding to the selected SSblock.

If SS block is associated with dedicated PRACH resources (PRACHoccasions), the UE selects a PRACH resource (PRACH occasion) fromdedicated PRACH resources otherwise the UE selects a PRACH resource(PRACH occasion) from contention based PRACH resources (PRACH occasions)corresponding to the selected SS block. The UE may select the earliestavailable PRACH resource (PRACH occasion) (dedicated if availableotherwise contention) of PRACH resources (PRACH occasions) correspondingto the selected SS block. In an embodiment, the UE may select randomlyone PRACH resource (or PRACH occasion) from configured PRACH resources(or PRACH occasions) (dedicated if available otherwise contention)corresponding to the selected SS block. In case multiple frequencydivision multiplexed PRACH resources (PRACH occasions) are available intime corresponding to the selected SS block, the UE randomly selectswith equal probability one PRACH resource (PRACH occasion) fromavailable multiple frequency division multiplexed PRACH resources (PRACHoccasions). The UE randomly selects with equal probability a PRACHpreamble from configured set of PRACH preambles.

For calculating the power for transmitting the PRACH, the UE estimatesthe path loss based on signals received in the selected SS block. Aftertransmitting the Msg1, the UE determines whether a RAR (i.e., Msg2)corresponding to Msg1 transmission is successfully received at operation2106. If the UE successfully receives the RAR, there is no need toretransmit Msg1 at operation 2107. If the UE is not able to receive theRAR, the UE determines whether the UE has performed maximum number ofallowed Msg1 transmissions at operation 2108. The UE retransmits theMsg1 if the UE has not yet transmitted maximum number of allowed Msg1transmissions. If the UE has performed maximum number of allowed Msg1transmissions, the UE does not retransmit Msg1. During theretransmission, the UE determines whether signal quality of SS blockselected for previous Msg1 transmission is greater than or equal to athreshold ‘SSBlockThreshold’ at operation 2109. If the signal quality ofthe SS block selected for the previous Msg1 transmission is greater thanor equal to the threshold ‘SSBlockThreshold’ the UE does not reselectthe SS block. The threshold can be configured by network in systeminformation (e.g., together with PRACH configuration or in RMSI) orhandover command or in dedicated RRC signaling. The UE uses the same SSblock as selected for the previous transmission for PRACH preambleand/or PRACH resource selection and path loss estimation forretransmission (i.e., next Msg1 transmission). During theretransmission, if the signal quality of the SS block selected for theprevious Msg1 transmission is less than the threshold‘SSBlockThreshold’, the UE may reselect SS block at operation 2110. TheUE may select a suitable SS block. In case suitable SS block is notfound, the UE may reselect a suitable SS block during retransmission.

In an alternate embodiment of this method, instead of SS block, CSI-RScan be used. UE selects CSI-RS instead of SS block using same procedureas explained above for SS block. The UE may select PRACH preamble and/orPRACH resource (or PRACH occasion) from PRACH preambles and/or PRACHresources (or PRACH occasion) corresponding to the selected CSI-RS. Allof the above procedures (Methods 1-17) can be replaced with the case ofCSI-RS and thresholds signaled for the case of CSI-RS can be used. Thiscan be done for the case of handover and the beam recovery cases whereinCSI-RS based RACH is suitable. Some procedures based on CSI-RS aredescribed below, but which have fallback mechanisms based on the SSblock wherein the RACH procedure fails or reaches maximum limit when itis performed using the CSI-RS resources.

Method 18:

FIG. 22 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 18 according to an embodiment of thedisclosure.

Referring to FIG. 22 , UE selects a suitable CSI-RS block for PRACHpreamble transmission. This procedure is similar to the case of the SSblock based RACH. The changes in the mentioned procedure occur when themaximum retransmission limit for the Msg1 is reached when CSI-RS isused. Then fallback RACH procedures for the UE may be supported by thegNB in order to allow for zero interruption time in handover scenarios.First the UE checks whether the CF RACH procedure based on the SS blocksof the target cell is supported at operation 2207. If it is supported,then it performs one of the CF methods based on SS blocks describedearlier at operation 2208. If it is not configured and indicated to theUE via the handover command; then the UE must perform contention-based4-step RACH procedure based on SS blocks of the target cell at operation2209. The configuration for the same can be obtained by reading the SIof the target cell. For the case when the UE has to perform thecontention-based RACH procedure, it can use the methods 1-6 mentionedearlier. The same mechanism can be used when the UE finds that theCSI-RS measurements are not crossing the suitable threshold levels.Either it can just continue to the perform RACH hoping that the RACHwould succeed; else it can fallback to SS-based RACH or it can trigger aUE may trigger RLF (i.e., connection re-establishment) for connectedstate. The key points to be noted for this procedure are the selectionof CSI-RS block with highest CSI-RS block RSRP amongst the CSI-RS blocksfor which CF resources are configured; the fact that the same CSI-RSblock is used for Msg1 (re-) transmission during a CF random accessprocedure and that the selection of PRACH preamble and/or PRACH resourcecorresponding to selected CSI-RS block from CF resources configured forthe UE must be used.

In this procedure, the UE selects a suitable CSI-RS or the CSI-RS withhighest CSI-RS RSRP amongst the CSI-RS for which CF resources areconfigured at operation 2201, the UE selects a dedicated PRACH preambleand/or PRACH resource corresponding to the selected CSI-RS at operation2202, and the UE transmits a PRACH preamble (i.e., Msg1) using theselected PRACH preamble and/or PRACH resource corresponding to theselected CSI-RS resource at operation 2203.

If CSI-RS resource is associated with a dedicated preamble the UE usesthat PRACH preamble. Otherwise, the UE selects a PRACH preamble randomlyfrom the contention based PRACH preambles corresponding to the selectedCSI-RS resources or from the entire pool of CF preambles.

If CSI-RS resource is associated with dedicated PRACH resources (PRACHoccasions), the UE selects a PRACH resource from it otherwise the UEselects a PRACH resource (PRACH occasion) from contention based PRACHresources (PRACH occasions) corresponding to the selected CSI-RSresource or from the entire pool of dedicated set of resources (PRACHoccasions) intended for the case of handover RACH.

After transmitting the Msg1, the UE determines whether a RAR (i.e.,Msg2) corresponding to Msg1 transmission is successfully received atoperation 2204. If the UE successfully receives the RAR, there is noneed to retransmit Msg1 at operation 2205. If the UE is not able toreceive the RAR, the UE determines whether the UE has performed maximumnumber of allowed Msg1 transmissions at operation 2206. The UEretransmits the Msg1 if the UE has not yet transmitted maximum number ofallowed Msg1 transmissions. If the UE has performed maximum number ofallowed Msg1 transmissions, fallback is needed.

For the case when fallback is needed, the UE sends a PRACH preamble(i.e., Msg1) using the selected PRACH preamble and/or PRACH resourcecorresponding to the selected SS block at operation 2208 or 2209.

If SS block is associated with a dedicated preamble the UE uses thatPRACH preamble. Otherwise, the UE selects a PRACH preamble randomly fromthe contention based PRACH preambles corresponding to the selected SSblock.

If SS block is associated with dedicated PRACH resources (PRACHoccasions), the UE selects a PRACH resource (PRACH occasion) from thissubset otherwise the UE selects a PRACH resource (PRACH occasion) fromcontention based PRACH resources (PRACH occasions) corresponding to theselected SS block. The UE may select the earliest available time slotcarrying a PRACH resource (dedicated if available otherwise contention)from PRACH resources (PRACH occasions) corresponding to the selected SSblock. In an embodiment, the UE may select randomly one PRACH resource(or PRACH occasion) from configured PRACH resources (or PRACH occasions)(dedicated if available otherwise contention) corresponding to theselected SS block. In case multiple frequency division multiplexed PRACHresources (PRACH occasions) are available in the time corresponding tothe selected SS block, the UE randomly selects with equal probabilityone PRACH resource (PRACH occasion) multiple frequency divisionmultiplexed from available PRACH resources (PRACH occasion). The UErandomly selects with equal probability a PRACH preamble from configuredset of PRACH preambles.

These resources for the case of SS block can be either CF based or CBbased appropriately as the decision taken by the UE.

Method 19:

FIG. 23 illustrates the UE behavior for the RACH transmission andre-transmission based on Method 19 according to an embodiment of thedisclosure.

Referring to FIG. 23 , UE selects a suitable CSI-RS block for PRACHpreamble transmission at operation 2301. This procedure is similar tothe case of the SS block based RACH. The changes in the mentionedprocedure occur when the UE finds that the CF resources for the case ofCSI-RS based RACH are not configured to the UE at operation 2302. Insuch case the UE must fall back to the SS based RACH resources either CFat operation 2304 or the contention-based at operation 2305. The UE canuse this behavior even in cases where it finds that the SS based RACHresources are available first in time as opposed to the CSI-RSresources. This can help UE save access latency and minimize thehandover interruption time.

In this procedure, the UE selects a suitable CSI-RS or the CSI-RS withhighest CSI-RS RSRP amongst the reported CSI-RS measurements atoperation 2301, and the UE determines whether CF PRACH preambles and/orPRACH resources are configured for the selected CSI-RS resource atoperation 2302. If the UE is configured with contention free (i.e.,dedicated) PRACH preamble and/or PRACH resource corresponding to theselected CSI-RS block, the UE selects dedicated PRACH preamble and/orPRACH resource corresponding to the selected block at operation 2306,and the UE transmits a PRACH preamble (i.e., Msg1) using the selectedPRACH preamble and/or PRACH resource corresponding to the selectedCSI-RS resource at operation 2307.

If CSI-RS resource is associated with a dedicated preamble the UE usesthat PRACH preamble. Otherwise, the UE selects a PRACH preamble randomlyfrom the contention based PRACH preambles corresponding to the selectedCSI-RS resources or from the entire pool of CF preambles.

If CSI-RS resource is associated with dedicated PRACH resources (PRACHoccasions), the UE selects a PRACH resource from it otherwise the UEselects a PRACH resource (PRACH occasion) from contention based PRACHresources (PRACH occasions) corresponding to the selected CSI-RSresource or from the entire pool of dedicated set of resources (PRACHoccasions) intended for the case of handover RACH.

After transmitting the Msg1, the UE determines whether a RAR (i.e.,Msg2) corresponding to Msg1 transmission is successfully received atoperation 2308. If the UE successfully receives the RAR, there is noneed to retransmit Msg1 at operation 2309. If the UE is not able toreceive the RAR, the UE determines whether the UE has performed maximumnumber of allowed Msg1 transmissions at operation 2310. The UEretransmits the Msg1 if the UE has not yet transmitted maximum number ofallowed Msg1 transmissions. If the UE has performed maximum number ofallowed Msg1 transmissions, the UE does not retransmit Msg1.

If the UE is not configured with contention free (i.e., dedicated) PRACHpreamble and/or PRACH resource, fallback is need. For the case whenfallback is needed, the UE checks whether the CF RACH procedure based onthe SS blocks of the target cell is supported at operation 2303, and theUE sends a PRACH preamble (i.e., Msg1) using the selected PRACH preambleand/or PRACH resource corresponding to the selected SS block operation2304 or 2305.

If SS block is associated with a dedicated preamble the UE uses thatPRACH preamble. Otherwise, the UE selects a PRACH preamble randomly fromthe contention based PRACH preambles corresponding to the selected SSblock.

If SS block is associated with dedicated PRACH resources (PRACHoccasions), the UE selects a PRACH resource (PRACH occasion) from thissubset otherwise the UE selects a PRACH resource (PRACH occasion) fromcontention based PRACH resources (PRACH occasions) corresponding to theselected SS block. The UE may select the earliest available time slotcarrying a PRACH resource (dedicated if available otherwise contention)from PRACH resources (PRACH occasions) corresponding to the selected SSblock. In an embodiment, the UE may select randomly one PRACH resource(or PRACH occasion) from configured PRACH resources (or PRACH occasions)(dedicated if available otherwise contention) corresponding to theselected SS block. In case multiple frequency division multiplexed PRACHresources (PRACH occasions) are available in the time corresponding tothe selected SS block, the UE randomly selects with equal probabilityone PRACH resource (PRACH occasion) multiple frequency divisionmultiplexed from available PRACH resources (PRACH occasion). The UErandomly selects with equal probability a PRACH preamble from configuredset of PRACH preambles.

These resources for the case of SS block can be either CF based or CBbased appropriately as the decision taken by the UE.

Method 20:

FIGS. 24A and 24B illustrate the UE behavior for the RACH transmissionand re-transmission based on Method 20 according to an embodiment of thedisclosure.

Referring to FIGS. 24A and 24B, UE selects a suitable CSI-RS block forPRACH preamble transmission. This procedure is similar to the case ofthe SS block based RACH. The changes in the mentioned procedure occurwhen the UE intends to perform re-transmission of the RACH preamble forthe case of CF RACH or even beam recovery based RACH at operation 2411.When the signal quality of the selected CSI-RS beam/resource is now notdeemed feasible for the case of re-transmission, then the UE may performre-selection of the CSI-RS resource at operation 2412. In other words,the UE can either re-perform measurements for the CSI-RS resources orthe UE can rely on past measurements of other CSI-RS resources which canbe beneficial if one of the beams may be blocked due to suddenenvironment changes. For calculating the power for transmitting thePRACH, the UE estimates the path loss based on signals received inselected CSI-RS resources.

In this procedure, the UE selects a suitable CSI-RS or the CSI-RS withhighest CSI-RS RSRP amongst the reported CSI-RS measurements atoperation 2401, and the UE determines whether CF PRACH preambles and/orPRACH resources are configured for the selected CSI-RS resource atoperation 2402. If the UE is configured with contention free (i.e.,dedicated) PRACH preamble and/or PRACH resource corresponding to theselected CSI-RS block, the UE selects dedicated PRACH preamble and/orPRACH resource corresponding to the selected block at operation 2406,and the UE transmits a PRACH preamble (i.e., Msg1) using the selectedPRACH preamble and/or PRACH resource corresponding to the selectedCSI-RS resource at operation 2407.

If CSI-RS resource is associated with a dedicated preamble the UE usesthat PRACH preamble. Otherwise, the UE selects a PRACH preamble randomlyfrom the contention based PRACH preambles corresponding to the selectedCSI-RS resources or from the entire pool of CF preambles.

If CSI-RS resource is associated with dedicated PRACH resources (PRACHoccasions), the UE selects a PRACH resource from it otherwise the UEselects a PRACH resource (PRACH occasion) from contention based PRACHresources (PRACH occasions) corresponding to the selected CSI-RSresource or from the entire pool of dedicated set of resources (PRACHoccasions) intended for the case of handover RACH.

After transmitting the Msg1, the UE determines whether a RAR (i.e.,Msg2) corresponding to Msg1 transmission is successfully received atoperation 2408. If the UE successfully receives the RAR, there is noneed to retransmit Msg1 at operation 2409. If the UE is not able toreceive the RAR, the UE determines whether the UE has performed maximumnumber of allowed Msg1 transmissions at operation 2410. The UEretransmits the Msg1 if the UE has not yet transmitted maximum number ofallowed Msg1 transmissions. If the UE has performed maximum number ofallowed Msg1 transmissions, the UE does not retransmit Msg1. During theretransmission, the UE determines whether signal quality of CSI-RS blockselected for previous Msg1 transmission is greater than or equal to aCSI-RS block threshold at operation 2411. If the signal quality of theCSI-RS block selected for the previous Msg1 transmission is greater thanor equal to the threshold, the UE does not reselect the CSI-RS block. Ifthe signal quality of the SS block selected for the previous Msg1transmission is less than the threshold, the UE may reselect CSI-RSblock at operation 2412. The UE may select the CSI-RS block with highestsignal quality amongst all CSI-RS blocks transmitted by gNB. In anotherembodiment, the UE may select the SS block with highest signal qualityamongst all CSI-RS blocks for which measurements are available.

If the UE is not configured with contention free (i.e., dedicated) PRACHpreamble and/or PRACH resource, fallback is need. For the case whenfallback is needed, the UE checks whether the CF RACH procedure based onthe SS blocks of the target cell is supported at operation 2403, and theUE sends a PRACH preamble (i.e., Msg1) using the selected PRACH preambleand/or PRACH resource corresponding to the selected SS block atoperation 2404 or 2405.

If SS block is associated with a dedicated preamble the UE uses thatPRACH preamble. Otherwise, the UE selects a PRACH preamble randomly fromthe contention based PRACH preambles corresponding to the selected SSblock.

If SS block is associated with dedicated PRACH resources (PRACHoccasions), the UE selects a PRACH resource (PRACH occasion) from thissubset otherwise the UE selects a PRACH resource (PRACH occasion) fromcontention based PRACH resources (PRACH occasions) corresponding to theselected SS block. The UE may select the earliest available time slotcarrying a PRACH resource (dedicated if available otherwise contention)from PRACH resources (PRACH occasions) corresponding to the selected SSblock. In an embodiment, the UE may select randomly one PRACH resource(or PRACH occasion) from configured PRACH resources (or PRACH occasions)(dedicated if available otherwise contention) corresponding to theselected SS block. In case multiple frequency division multiplexed PRACHresources (PRACH occasions) are available in the time corresponding tothe selected SS block, the UE randomly selects with equal probabilityone PRACH resource (PRACH occasion) multiple frequency divisionmultiplexed from available PRACH resources (PRACH occasion). The UErandomly selects with equal probability a PRACH preamble from configuredset of PRACH preambles.

These resources for the case of SS block can be either CF based or CBbased appropriately as the decision taken by the UE.

Multiple Msg1 Transmissions Before or while Waiting for RAR for FirstTransmitted Msg 1

Tx/Rx beam correspondence at UE holds if at least one of the followingis satisfied: UE is able to determine a UE Tx beam for the uplinktransmission based on UE's downlink measurement on UE's one or more Rxbeams. UE is able to determine a UE Rx beam for the downlink receptionbased on transmission/reception point (TRP)'s indication based on uplinkmeasurement on UE's one or more Tx beams. Tx/Rx beam correspondence atUE holds or not depends on UE capability.

For contention free scenario (e.g., handover), UE is configured with adedicated preamble. If TX/RX correspondence is not there at UE then UEneeds to transmit PRACH message 1 (i.e., dedicated PRACH preamble) usingmultiple UE TX beams as UE does not know the specific UE TX beam,transmission from which can be received by gNB.

FIG. 25 illustrates an example where UE performs only one Msg. 1transmission before RAR window.

Referring to FIG. 25 , UE transmits PRACH message 1 using a UE TX beamin RACH transmission occasion and wait for RAR in RAR window. If RAR isnot received, UE transmit PRACH message 1 using another UE TX beam inanother RACH transmission occasion and so on. This may significantlydelay access to target cell.

The delay can be reduced if UE is allowed to transmit PRACH preamble inmore than one RACH transmission occasion before monitoring the RARwindow.

FIGS. 26A and 26B illustrate two examples of multiple Msg. 1transmissions before RAR window according to various embodiments of thedisclosure.

Referring to FIG. 26A, UE transmits Msg. 1 in RACH transmissionoccasions which are configured in frequency domain. This is possibleonly if UE has multiple antenna panels as UE can generate beam in onlyone direction using a single antenna panel. Referring to FIG. 26B, UEtransmits Msg. 1 in RACH transmission occasions which are configured intime domain. A UE without beam correspondence can transmit Msg. 1 viadifferent UL TX beams in different RACH TX occasion and access thetarget cell with less delay.

One of the issues in the above scenario is RAR monitoring (i.e., whetherthere is a single RAR window or separate RAR window for each transmittedMSG1). It is proposed that UE can monitor the RAR window(s) forreceiving RAR when it transmits multiple Msg1 in one of the followingways:

The number of Msg1s UE can transmit before or while monitoring the RARwindow can be configured by the network (e.g., in system information orRRC signaling or handover command) by network.

Option 1:

FIG. 27 illustrates multiple Msg1 transmissions before or while waitingfor RAR for first transmitted Msg1 based on Option 1 according to anembodiment of the disclosure.

Referring to FIG. 27 , UE transmits first Msg1 in a transmission timeinterval (TTI) X. The transmission occasion(s) where UE can transmit1^(st) Msg1 can be indicated by network.

The RAR window starts from TTI X+offset where offset can be pre-definedor configured (e.g., in system information or RRC signaling or handovercommand) by network. Offset can be zero. RAR window ends at TTI Z whereTTI Z equal to TTI X+offset+RAR Window length where RAR Window length isconfigured (e.g., in system information or RRC signaling) by network.From TTI X+1 to TTI Z-offset, UE can transmit additional MSG1s inavailable PRACH TX occasion. For each additional Msg1 transmitted by UE,from TTI X+1 to TTI Z-offset, UE monitors RAR in RAR window (i.e., fromTTI X+offset to TTI X+offset+RAR Window length). UE will monitor for RARcorresponding to RA-RNTI and RAPID of each transmitted Msg1. As soon asUE receives RAR for any Msg1 transmitted by UE, it shall consider RARreception successful and will not transmit additional Msg1 in intervalTTI X+1 to TTI Z-offset.

Option 2:

FIGS. 28 and 29 illustrate multiple Msg1 transmissions before or whilewaiting for RAR for first transmitted Msg1 based on Option 2 accordingto an embodiment of the disclosure.

In this method, one or more sets of RACH TX occasions are configured bynetwork (e.g., in system information or RRC signaling or handovercommand). Each set comprise of N TX occasions. N is configurable bynetwork. N can be configured based on number of TX beams at UE which UEmay report to gNB in capability signaling. The TX occasions in each setcan be contiguous or may not be contiguous. Each set of TX occasions maybe associated with a SS block or CSI-RS in order to indicate the DL TXbeam. In case of such association, SS block ID or CSI-RS ID associatedwith each set is indicated by network. Alternately, each TX occasion ina set may be associated with a SS block or CSI-RS in order to indicatethe DL TX beam wherein one or multiple TX occasions may be associatedwith same SS block or CSI-RS. Alternately, TX occasions are not mappedto SS block or CSI-RS. UE may be assigned preamble corresponding to SSblock or CSI-RS wherein this assignment can be for some SS blocks orCSI-RSs.

UE transmits MSG1s using a set of TX occasions. RAR window starts at anoffset from end of set of RACH TX occasions as shown in FIG. 28 .

UE will monitor for RAR corresponding to RA-RNTI and RAPID of eachtransmitted Msg1 in RAR window. As soon as UE receives RAR for any Msg1transmitted by UE, it shall consider RAR reception successful. Inalternate embodiment, RAR window starts at an offset from end of firstRACH TX occasion in set of RACH TX occasions as shown in FIG. 29 .

Option 3:

FIG. 30 illustrates multiple Msg1 transmissions before or while waitingfor RAR for first transmitted Msg1 based on Option 3 according to anembodiment of the disclosure.

In this method no special signaling such as indication of TX occasionsfor 1^(st) msg1 as in option 1 or set of TX occasions as in option 2 areneeded. PRACH resources can be configured in same manner irrespective ofwhether UE is allowed to transmit multiple Msg1 or not. In this methodfor every MSG1 transmitted by UE there is independent RAR window. Incase of multiple MSG1 s transmitted by UE, UE will monitor RAR inmultiple RAR windows wherein RAR windows can be overlapping. UE willmonitor for RAR corresponding to RA-RNTI and RAPID of each transmittedMsg1 in corresponding RAR window. As soon as UE receives RAR for anyMsg1 transmitted by UE, it shall consider RAR reception successful.

Prioritization Between Msg1 Based SI Request and RRC ConnectionRequest/RRC Connection Resume Request by UE in RRC Idle or InactiveState.

Scenario: UE has initiated SI acquisition on an on demand-basis. Randomaccess procedure (2 step Msg1 based SI request or 4 step Msg3 based SIrequest) to transmit SI request is initiated. The SI request procedureor random access procedure is completed when UE receives theacknowledgement (in Msg2 for Msg1 based SI request; in Msg4 for Msg4based SI request) for SI request transmitted by UE. After the completionof SI request procedure UE monitor one or more SI Window(s) of requestedSI message(s) to receive the requested SI message(s). During the timeinterval from initiation of SI request and reception of acknowledgmentfor SI request, UE may trigger connection request/connection resumerequest. The trigger may be due to location update or RAN area update orpaging reception or mobile originated call or for any other reason asspecified in specification. Since the SI request procedure is ongoing,connection setup can happen after the completion of SI requestprocedure. This may however delay the connection setup.

In one embodiment of the proposed disclosure, it is proposed that the UEprioritizes the connection setup (i.e., connection request/connectionresume request) over the SI request. UE terminates the ongoing SIrequest procedure and initiates transmission of connectionrequest/connection resume request. In case of Msg1 based SI request,ongoing random access procedure to transmit the SI request isterminated. Random access procedure for transmitting the connectionrequest/connection resume request is initiated by UE. In case of Msg3based SI request, ongoing random access procedure to transmit the SIrequest is not terminated. During the ongoing random access procedureconnection request/connection resume request is transmitted. SI requestis transmitted after setting up the connection.

In one implementation, RRC has initiated transmission of SI request.While RRC is waiting for SI request acknowledgement from lower layers,RRC connection request/resume request is triggered (e.g., based onindication from higher layer). RRC in UE inform lower layers (i.e., MAC)to terminate transmission of SI request. RRC submits RRC connectionrequest/RRC connection resume request to lower layer for transmission.In case of Msg1 based SI request, MAC layer terminates ongoing RAprocedure for msg1 based SI request based on indication from higherlayer (i.e., RRC). In case of Msg3 based SI request, MAC layer continuesongoing RA procedure and connection request/connection resume request istransmitted during the random access procedure.

In another embodiment of the proposed disclosure, it is proposed that ifSI request is initiated for acquiring one or more SIs which areessential or which (e.g., access control parameters) are needed forconnection setup then UE prioritizes SI request over RRC connectionrequest/resume request. UE does not terminate on going SI request. If SIrequest is initiated for acquiring one or more SIs which are notessential or which are not needed for connection setup then UEprioritizes RRC connection request/resume request over SI request. UEterminates the ongoing SI request procedure and initiates transmissionof connection request/connection resume request. In case of Msg1 basedSI request, ongoing random access procedure to transmit the SI requestis terminated. Random access procedure for transmitting the connectionrequest/connection resume request is initiated by UE. In case of Msg3based SI request, ongoing random access procedure to transmit the SIrequest is not terminated. During the ongoing random access procedureconnection request/connection resume request is transmitted. SI requestis transmitted after setting up the connection.

In another embodiment of the proposed disclosure, it is proposed thatthe UE prioritizes the connection setup (i.e., connectionrequest/connection resume request) over the SI request if connectionsetup is for one or more pre-defined access categories or if connectionsetup is for certain access categories of high priority (e.g., prioritygreater than a specified value) or if connection setup is for one ormore services defined in specification for which connection setup ismore prioritized than SI request. UE terminates the ongoing SI requestprocedure and initiates transmission of connection request/connectionresume request. In case of Msg1 based SI request, ongoing random accessprocedure to transmit the SI request is terminated. Random accessprocedure for transmitting the connection request/connection resumerequest is initiated by UE. In case of Msg3 based SI request, ongoingrandom access procedure to transmit the SI request is not terminated.During the ongoing random access procedure connection request/connectionresume request is transmitted. SI request is transmitted after settingup the connection.

In one embodiment of the proposed disclosure, network may indicate in SIwhether UE needs to prioritize the connection setup (i.e., connectionrequest/connection resume request) over the SI request.

Distinguishing Msg 4 for SI Request from Msg 4 for ConnectionRequest/Connection Resume Request Sent in Msg3:

Scenario:

After the successful reception of RAR, UE sends Msg3 in UL grantreceived in RAR. Msg3 includes common control channel (CCCH) servicedata unit (SDU) (i.e., system information request message). Systeminformation request message is generated by RRC. The information aboutthe SIB(s) used by UE is included in system information request message.There can be collision between UE1 transmitting SI request in Mgs3 andanother UE2 transmitting other RRC message (such as connection request)in Msg3, if both UE1 and UE2 has transmitted Msg1 using same PRACHpreamble and PRACH resource and has received the RAR. Msg3 from one ofthe UEs may be successful. gNB will transmit the Msg4 in response toreceived Msg3. Contention resolution MAC control element (CE) carrying xbits (48 bits in LTE) of CCCH SDU received in Msg3 is included in Msg4.The transport block (TB) carrying Contention resolution MAC CE isscheduled by physical downlink control channel (PDCCH) addressed totemporary-cell radio network temporary identifier (T-CRNTI) (Note thatT-CRNTI was sent earlier to UE by gNB in RAR). In the TB scheduled byPDCCH addresses to T-CRNTI, MAC layer in UE checks if the MAC PDUincludes a contention resolution MAC CE. X bits of CCCH SDU in Msg3 forSI request and X bits of CCCH SDU in Msg3 for connection request (orother message) can be same. So there can be ambiguity in determiningwhether the received Msg4 corresponds to its Msg3 or not.

In one embodiment of the proposed disclosure, it is proposed that SIrequest should include UE Identity (e.g., international mobilesubscriber identity (IMSI) or system architecture evolution-temporarymobile subscriber identity (S-TMSI) or subscriber permanent identifier(SUPI) or any other UE identity defined in system) in addition toinformation about the SIB(s) used by UE. In the above scenario, thiswill ensure that, X bits of CCCH SDU in Msg3 for SI request transmittedby UE1 and X bits of CCCH SDU in Msg3 for connection request (or othermessage) transmitted by UE2 is not same. If gNB has received Msg3carrying SI request from UE1, UE1 will receive Msg4 and contents ofContention resolution MAC CE will match with x bits of CCCH SDUtransmitted by it in Msg3. UE2 may also receive Msg4 (as T-CRNTI wasreceived by both UE1 and UE2) but contents of Contention resolution MACCE will not match with x bits of CCCH SDU transmitted by it in Msg3. IfgNB has received Msg3 carrying connection request from UE2, UE2 willreceive Msg4 and contents of Contention resolution MAC CE will matchwith x bits of CCCH SDU transmitted by it in Msg3. UE1 may also receiveMsg4 but contents of Contention resolution MAC CE will not match with xbits of CCCH SDU transmitted by it in Msg3.

In alternate embodiment of the proposed disclosure, it is proposed thatUE identity is not included in system information request message. Twotypes of MAC CE are defined for including in Msg4. One for the case whenMsg4 is transmitted in response to reception of Msg3 with SI request andanother for the case when Msg4 is transmitted in response to receptionof Msg3 with message (e.g., connection request, connection resumerequest) other than SI request. In one embodiment, the logical channelidentifier (LCID) reserved for both MAC CEs to be included in MACsubheader of MAC CE is same and a type field is included in contents ofMAC CE. This type field distinguishes whether this MAC CE is in responseto SI request or not. In another embodiment, distinct LCIDs are reservedfor each MAC CE. One MAC CE is contention resolution MAC CE and anotherMAC CE is SI ACK MAC CE. Msg4 for connection request/resume request inMsg3 will include contention resolution MAC CE. Msg4 for SI request inMsg3 will include SI ACK MAC CE. Contention resolution MAC CE includes xbits of CCCH SDU included in Msg3. SI ACK MAC CE includes x bits of CCCHSDU included in Msg3. Alternately SI ACK MAC CE includes list of one ormore SIB types or SI message index. Alternately SI ACK MAC CE includes abit map wherein each bit corresponds to a SIB or SI message. Forexample, if bit map is b0b1b2b3b4, then MSB (b0) in bit map correspondsto first SI message (or SIB type) in list of SI messages (or SIB types)in SIB1, b1 in bitmap corresponds to second SI message (or SIB type) inlist of SI messages (or SIB types) in SIB1 and so on. Alternately, ifbit map is b0b1b2b3b4, then least significant bit (LSB) (b4) in bit mapcorresponds to first SI message (or SIB type) in list of SI messages (orSIB types) in SIB1, b3 in bitmap corresponds to second SI message (orSIB type) in list of SI messages (or SIB types) in SIB1 and so on. Thelength of bit map in MAC CE can be fixed. Alternately length of bit mapin MAC CE can be variable. Length can be equal to number of SI messages(or SIB types) in list of SI messages (or SIB types) in SIB1.

Pre-Emption Indication and DRX Inactivity Timer Handling

Scenario:

gNB schedules a packet (DL or UL) by transmitting PDCCH. During the OnDuration of DRX cycle, gNB starts (if not already running) or resets (ifinactivity timer was already running) the inactivity timer. In order toavoid collision between URLL packet and eMBB packet, gNB may latertransmit a Pre-emption indication to skip (or abort) reception ofscheduled DL packet or skip transmission of scheduled UL packet. GNB mayor may not schedule the aborted packet again later.

In one embodiment of the proposed disclosure, it is proposed that if UEreceives a pre-emption indication aborting the scheduled packettransmission or reception, UE should stop the inactivity timer (ifrunning) if the inactivity timer was started when the PDCCH schedulingthe aborted packet was received. In another embodiment of the proposeddisclosure, it is proposed that if UE receives a pre-emption indicationaborting the scheduled packet transmission or reception, UE should stopthe inactivity timer (if running) if the inactivity timer was startedwhen the PDCCH scheduling the aborted packet was received and the timeinterval elapsed since the starting of timer is greater than a thresholdor is smaller than a threshold. Threshold can be pre-defined or signaledby network.

FIG. 31 is a block diagram of a UE according to an embodiment of thedisclosure.

Referring to FIG. 31 , the UE includes a transceiver 3110, a controller3120 and a memory 3130. The transceiver 3110, the controller 3120 andthe memory 3130 are configured to perform the above described operationsof the UE. Although the transceiver 3110, the controller 3120 and thememory 3130 are shown as separate entities, they may be realized as asingle entity like a single chip. The transceiver 3110, the controller3120 and the memory 3130 may be electrically connected to or coupledwith each other.

The transceiver 3110 may transmit and receive signals to and from othernetwork entities, e.g., a BS.

The controller 3120 may control the UE to perform a function accordingto one of the embodiments described above. For example, the controller3120 may be configured to control the transceiver to receiveconfiguration information on RA resources associated withsynchronization signal (SS) blocks from the base station, control thetransceiver to receive one or more SS blocks from the base station,determine whether there is at least one suitable SS block for whichcontention free RA resources are configured amongst the one or more SSblocks based on the configuration information, select a suitable SSblock for which contention free RA resources are configured if there isat least one suitable SS block for which contention free RA resourcesare configured amongst the one or more SS blocks, select a first RApreamble corresponding to the selected suitable SS block, and controlthe transceiver to transmit the first RA preamble to the base station.The controller 3120 may be further configured to select a suitable SSblock for which contention based RA resources are configured if asuitable SS block for which contention free RA resources are configuredamongst the one or more SS blocks is not found. The controller 3120 maybe configured to determine a SS block of the one or more SS blocks as asuitable SS block if a signal quality of the SS block is greater than athreshold configured in a radio resource control (RRC) signaling. Thecontroller 3120 may be further configured to select a next availabletime slot carrying a RA resource from RA resources corresponding to theselected SS block. The controller 3120 may be further configured tocontrol the transceiver to transmit a second RA preamble to the basestation, and monitor responses to the first RA preamble and the secondRA preamble in a RAR window, wherein the RAR window is started after thetransmitting of the first RA preamble after an offset. The controller3120 may refer to a circuitry, an ASIC, or at least one processor.

In an embodiment, the operations of the UE may be implemented using thememory 3130 storing corresponding program codes. Specifically, the UEmay be equipped with the memory 3130 to store program codes implementingdesired operations. To perform the desired operation, the controller3120 may read and execute the program codes stored in the memory 3130 byusing a processor or a central processing unit (CPU).

FIG. 32 is a block diagram of a BS according to an embodiment of thedisclosure.

Referring to FIG. 32 , a BS includes a transceiver 3210, a controller3220 and a memory 3230. The transceiver 3210, the controller 3220 andthe memory 3230 are configured to perform the above described operationsof the network (e.g., gNB). Although the transceiver 3210, thecontroller 3220 and the memory 3230 are shown as separate entities, theymay be realized as a single entity like a single chip. The transceiver3210, the controller 3220 and the memory 3230 may be electricallyconnected to or coupled with each other.

The transceiver 3210 may transmit and receive signals to and from othernetwork entities, e.g., a UE.

The controller 3220 may control the BS to perform a function accordingto one of the embodiments described above. For example, the controller3220 may be configured to control the transceiver to transmitconfiguration information on RA resources associated withsynchronization signal (SS) blocks to the terminal, control thetransceiver to transmit one or more SS blocks to the terminal, andcontrol the transceiver to receive an RA preamble from the terminal. Thecontroller 3220 may refer to a circuitry, an ASIC, or at least oneprocessor.

In an embodiment, the operations of the BS may be implemented using thememory 3230 storing corresponding program codes. Specifically, the BSmay be equipped with the memory 3230 to store program codes implementingdesired operations. To perform the desired operation, the controller3220 may read and execute the program codes stored in the memory 3230 byusing a processor or a CPU.

While the disclosure has been shown and described with reference tovarious embodiments thereof, it will be understood by those skilled inthe art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the disclosure as definedby the appended claims and their equivalents.

What is claimed is:
 1. A method performed by a terminal in a wirelesscommunication system, comprising: receiving, from a base station,configuration information on a contention-based random access (RA) andinformation on a threshold for a selection of a synchronization signal(SS) block; receiving, from the base station, configuration informationon a contention-free RA and information on at least one RA preambleassociated with each SS block; in case that the configurationinformation on the contention-free RA comprises information oncontention-free RA resources associated with SS blocks and at least oneSS block with a signal quality greater than the threshold among the SSblocks associated with the contention-free RA resources is available,selecting a first SS block among the at least one SS block associatedwith the contention-free RA resources; and selecting a first RA preamblecorresponding to the selected first SS block based on the information onthe at least one RA preamble associated with each SS block; in case thatthe at least one SS block with the signal quality greater than thethreshold among the SS blocks associated with the contention-free RAresources is not available, identifying that at least one SS block witha signal quality greater than the threshold among SS blocks associatedwith contention-based RA resources; selecting a second SS block amongthe at least one SS block associated with the contention-based RAresources; and selecting a second RA preamble randomly with equalprobability from at least one contention-based RA preamble associatedwith the selected second SS block; selecting a physical random accesschannel (PRACH) occasion based on the selected first SS block or theselected second SS block; and transmitting, to the base station, thefirst RA preamble or the second RA preamble in the selected PRACHoccasion.
 2. The method of claim 1, wherein the configurationinformation on the contention-based RA is included in a radio resourcecontrol (RRC) message.
 3. The method of claim 1, wherein the signalquality greater than the threshold is identified based on referencesignal received power (RSRP) of an SS block.
 4. The method of claim 1,further comprising: identifying a next available PRACH occasion fromamong PRACH occasions corresponding to the selected first SS block orthe selected second SS block.
 5. A method performed by a base station ina wireless communication system, comprising: transmitting, to a terminalin the wireless communication system, configuration information on acontention-based random access (RA) and information on a threshold for aselection of a synchronization signal (SS) block; transmitting, to theterminal, configuration information on a contention-free RA andinformation on at least one RA preamble associated with each SS block;and receiving, from the terminal, a first RA preamble or a second RApreamble in a physical random access channel (PRACH) occasion selectedbased on a first SS block or a second SS block, wherein in case that theconfiguration information on the contention-free RA comprisesinformation on contention-free RA resources associated with SS blocksand at least one SS block with a signal quality greater than thethreshold among the SS blocks associated with the contention-free RAresources, the first SS block is selected among the at least one SSblock associated with the contention-free RA resources and the first RApreamble corresponding to the selected first SS block based on theinformation on the at least one RA preamble associated with each SSblock, and wherein in case that the at least one SS block with thesignal quality greater than the threshold among the SS blocks associatedwith the contention-free RA resources is not available, at least one SSblock with a signal quality greater than the threshold among SS blocksassociated with contention-based RA resources is identified, the secondSS block is selected among the at least one SS block associated with thecontention-based RA resources, and the second RA preamble randomly withequal probability from at least one contention-based RA preambleassociated with the selected second SS block.
 6. The method of claim 5,wherein the configuration information on the contention-based RA isincluded in a radio resource control (RRC) message.
 7. The method ofclaim 5, wherein the signal quality greater than the threshold isidentified based on reference signal received power (RSRP) of an SSblock.
 8. A terminal in a wireless communication system, comprising: atransceiver; and a controller coupled with the transceiver andconfigured to: receive, from a base station, configuration informationon a contention-based random access (RA) and information on a thresholdfor a selection of a synchronization signal (SS) block, receive, fromthe base station, configuration information on a contention-free RA andinformation on at least one RA preamble associated with each SS block,in case that the configuration information on the contention-free RAcomprises information on contention-free RA resources associated with SSblocks and at least one SS block with a signal quality greater than thethreshold among the SS blocks associated with the contention-free RAresources is available, select a first SS block among the at least oneSS block associated with the contention-free RA resources, and select afirst RA preamble corresponding to the selected first SS block based onthe information on the at least one RA preamble associated with each SSblock, in case that at least one SS block with the signal qualitygreater than the threshold among the SS blocks associated with thecontention-free RA resources is not available, identify at least one SSblock with a signal quality greater than the threshold among SS blocksassociated with contention-based RA resources, select a second SS blockamong the at least one SS block associated with the contention-based RAresources, and select a second RA preamble randomly with equalprobability from at least one contention-based RA preamble associatedwith the selected second SS block, select a physical random accesschannel (PRACH) occasion based on the selected first SS block or theselected second SS block, and transmit, to the base station, the firstRA preamble or the second RA preamble in the selected PRACH occasion. 9.The terminal of claim 8, wherein the configuration information on thecontention-based RA is included in a radio resource control (RRC)message.
 10. The terminal of claim 8, wherein the controller is furtherconfigured to identify the signal quality greater than the thresholdbased on reference signal received power (RSRP) of an SS block.
 11. Theterminal of claim 8, wherein the controller is further configured toidentify a next available PRACH occasion from among PRACH occasionscorresponding to the selected first SS block or the selected second SSblock.
 12. A base station in a wireless communication system,comprising: a transceiver; and a controller coupled with the transceiverand configured to: transmit, to a terminal, configuration information ona contention-based random access (RA) and information on a threshold fora selection of a suitable SS block, transmit, to the terminal,configuration information on a contention-free RA and information on atleast one RA preamble associated with each SS block, and receive, fromthe terminal, a first RA preamble or a second RA preamble in a physicalrandom access channel (PRACH) occasion selected based on a first SSblock or a second SS block, wherein in case that the configurationinformation on the contention-free RA comprises information oncontention-free RA resources associated with SS blocks and at least oneSS block with a signal quality greater than the threshold among the SSblocks associated with the contention-free RA resources, the first SSblock is selected among the at least one SS block associated with thecontention-free RA resources and the first RA preamble corresponding tothe selected first SS block based on the information on the at least oneRA preamble associated with each SS block, and wherein in case that theat least one SS block with the signal quality greater than the thresholdamong the SS blocks associated with the contention-free RA resources isnot available, at least one SS block with a signal quality greater thanthe threshold among SS blocks associated with contention-based RAresources is identified, the second SS block is selected among the atleast one SS block associated with the contention-based RA resources,and the second RA preamble randomly with equal probability from at leastone contention-based RA preamble associated with the selected second SSblock.
 13. The base station of claim 12, wherein the configurationinformation on the contention-based RA is included in a radio resourcecontrol (RRC) message.
 14. The base station of claim 12, wherein thesignal quality greater than the threshold is identified based onreference signal received power (RSRP) of an SS block.
 15. The method ofclaim 1, further comprising: determining whether a random accessresponse (RAR) corresponding to the first RA preamble or the second RApreamble is not received and whether a maximum number of a RA preambletransmission is not reached; in case that the RAR is not received, themaximum number of the RA preamble transmission is not reached, theconfiguration information on the contention-free RA comprises theinformation on the contention-free RA resources associated with the SSblocks, and the at least one SS block with the signal quality greaterthan the threshold among the SS blocks associated with thecontention-free RA resources is available, selecting a third SS blockamong the at least one SS block associated with the contention-free RAresources; and selecting a third RA preamble corresponding to theselected third SS block based on the information on the at least one RApreamble associated with each SS block; selecting a PARCH occasion basedon the selected third SS block; and transmitting, to the base station,the third RA preamble in the selected PRACH occasion.
 16. The method ofclaim 15, further comprising: in case that the RAR is not received, themaximum number of the RA preamble transmission is not reached, and theat least one SS block with the signal quality greater than the thresholdamong the SS blocks associated with the contention-free RA resources isnot available, identifying that at least one SS block with the signalquality greater than the threshold among the SS blocks associated withcontention-based RA resources; selecting a fourth SS block among the atleast one SS block associated with the contention-based RA resource; andselecting a fourth RA preamble randomly with equal probability from atleast one contention-based RA preamble associated with the selectedfourth SS block; selecting a PARCH occasion based on the selected fourthSS block; and transmitting, to the base station, the fourth RA preamblein the selected PRACH occasion.
 17. The method of claim 5, furthercomprising: receiving, from the terminal, a third RA preamble in a PRACHoccasion selected based on a third SS block, in case that a randomaccess response (RAR) corresponding to the first RA preamble or thesecond RA preamble is not received, a maximum number of a RA preambletransmission is not reached, the configuration information on thecontention-free RA comprises the information on the contention-free RAresources associated with the SS blocks, and the at least one SS blockwith the signal quality greater than the threshold among the SS blocksassociated with the contention-free RA resources is available, whereinthe third SS block among the at least one SS block associated with thecontention-free RA resources is selected and the third RA preamblecorresponding to the selected third SS block is selected based on theinformation on the at least one RA preamble associated with each SSblock; or receiving, from the terminal, a fourth RA preamble in a PRACHoccasion selected based on a fourth SS block, in case that the RARcorresponding to the first RA preamble or the second RA preamble is notreceived, the maximum number of the RA preamble transmission is notreached, and the at least one SS block with the signal quality greaterthan the threshold among the SS blocks associated with thecontention-free RA resources is not available, wherein at least one SSblock with the signal quality greater than the threshold among the SSblocks associated with contention-based RA resources is identified, thefourth SS block among the at least one SS block associated with thecontention-based RA resource is selected, the fourth RA preamble isselected randomly with equal probability from at least onecontention-based RA preamble associated with the selected fourth SSblock.
 18. The terminal of claim 8, wherein the controller is furtherconfigured to: determine whether a random access response (RAR)corresponding to the first RA preamble or the second RA preamble is notreceived and whether a maximum number of a RA preamble transmission isnot reached, in case that the RAR is not received, the maximum number ofthe RA preamble transmission is not reached, the configurationinformation on the contention-free RA comprises the information on thecontention-free RA resources associated with the SS blocks, and the atleast one SS block with the signal quality greater than the thresholdamong the SS blocks associated with the contention-free RA resources isavailable, select a third SS block among the at least one SS blockassociated with the contention-free RA resources, and select a third RApreamble corresponding to the selected third SS block based on theinformation on the at least one RA preamble associated with each SSblock, select a PARCH occasion based on the selected third SS block, andtransmit, to the base station, the third RA preamble in the selectedPRACH occasion.
 19. The terminal of claim 18, wherein the controller isfurther configured to: in case that the RAR is not received, the maximumnumber of the RA preamble transmission is not reached, and the at leastone SS block with the signal quality greater than the threshold amongthe SS blocks associated with the contention-free RA resources is notavailable, identify that at least one SS block with the signal qualitygreater than the threshold among the SS blocks associated withcontention-based RA resources, select a fourth SS block among the atleast one SS block associated with the contention-based RA resource, andselect a fourth RA preamble randomly with equal probability from atleast one contention-based RA preamble associated with the selectedfourth SS block, select a PARCH occasion based on the selected fourth SSblock, and transmit, to the base station, the fourth RA preamble in theselected PRACH occasion.
 20. The base station of claim 12, wherein thecontroller is further configured to: receive, from the terminal, a thirdRA preamble in a PRACH occasion selected based on a third SS block, incase that a random access response (RAR) corresponding to the first RApreamble or the second RA preamble is not received, a maximum number ofa RA preamble transmission is not reached, the configuration informationon the contention-free RA comprises the information on thecontention-free RA resources associated with the SS blocks, and the atleast one SS block with the signal quality greater than the thresholdamong the SS blocks associated with the contention-free RA resources isavailable, wherein the third SS block among the at least one SS blockassociated with the contention-free RA resources is selected and thethird RA preamble corresponding to the selected third SS block isselected based on the information on the at least one RA preambleassociated with each SS block, or receive, from the terminal, a fourthRA preamble in a PRACH occasion selected based on a fourth SS block, incase that the RAR corresponding to the first RA preamble or the secondRA preamble is not received, the maximum number of the RA preambletransmission is not reached, and the at least one SS block with thesignal quality greater than the threshold among the SS blocks associatedwith the contention-free RA resources is not available, wherein at leastone SS block with the signal quality greater than the threshold amongthe SS blocks associated with contention-based RA resources isidentified, the fourth SS block among the at least one SS blockassociated with the contention-based RA resource is selected, the fourthRA preamble is selected randomly with equal probability from at leastone contention-based RA preamble associated with the selected fourth SSblock.